Inside the troubled nuclear power plant, officials knew the risks were high when they decided to vent radioactive steam from a severely overheated reactor vessel. They knew a hydrogen explosion could occur, and it did. The decision still trumped the worst-case alternative _ total nuclear meltdown. 
 
 In this photo taken on Aug. 10, 2006, the Fukushima Daini Nuclear Power Plant in Tmiokamachi, Fukushima Prefecture, is seen. The cooling ability had been lost at three of four reactors, in white and light... (Associated Press) 
 
 In this photo taken on Oct. 3, 2008, the Fukushima Daiichi Nuclear Power Plant in Okumamachi, Fukushima Prefecture, is seen. A strong earthquake on March 11, 2011 knocked out power at the plant, and because... (Associated Press) 
 
 Police officers wearing gas masks patrol in the area of the Fukushima power plant's Unit 1 in Okumamachi, Fukushima Prefecture (state), northern Japan, Saturday, March 12, 2011, amid fears that a part... (Associated Press) 
 
 Fukushima Daiichi power plant's Unit 1 is seen in Okumamachi, Fukushima prefecture, Japan, Friday, March 11, 2011. The nuclear power plant affected by a massive earthquake is facing a possible meltdown,... (Associated Press) 
 
 At least for the time being. 
 
 The chain of events started Friday when a magnitude-8.9 earthquake and tsunami severed electricity to the Fukushima Dai-ichi nuclear complex 170 miles (270 kilometers) northeast of Tokyo, crippling its cooling system. Then, backup power did not kick in properly at one of its units. 
 
 From there, conditions steadily worsened, although government and nuclear officials initially said things were improving. Hours after the explosion, they contended that radiation leaks were reduced and that circumstances had gotten better at the 460-megawatt Unit 1. But crisis after crisis continued to develop or be revealed. 
 
 Without power, and without plant pipes and pumps that were destroyed in the explosion of the most-troubled reactor's containment building, authorities resorted to drawing seawater in an attempt to cool off the overheated uranium fuel rods. 
 
 Robert Alvarez, senior scholar at the Institute for Policy Studies and former senior policy adviser to the U.S. secretary of energy, said in a briefing for reporters that the seawater was a desperate measure. 
 
 "It's a Hail Mary pass," he said. 
 
 He said that the success of using seawater and boron to cool the reactor will depend on the volume and rate of their distribution. He said the dousing would need to continue nonstop for days. 
 
 Another key, he said, was the restoration of electrical power, so that normal cooling systems can be restored. 
 
 Officials placed Dai-ichi Unit 1, and four other reactors, under states of emergency Friday because operators had lost the ability to cool the reactors using usual procedures. 
 
 An additional reactor was added to the list early Sunday, for a total of six _ three at the Dai-ichi complex and three at another nearby complex. Local evacuations have been ordered at each location. Japan has a total of 55 reactors spread across 17 complexes nationwide. 
 
 Officials began venting radioactive steam at Fukushima Dai-ichi's Unit 1 to relieve pressure inside the reactor vessel, which houses the overheated uranium fuel. 
 
 Concerns escalated dramatically Saturday when that unit's containment building exploded. 
 
 It turned out that officials were aware that the steam contained hydrogen, acknowledged Shinji Kinjo, spokesman for the government Nuclear and Industrial Safety Agency. More importantly, they also were aware they were risking an explosion by deciding to vent the steam. 
 
 The significance of the hydrogen began to come clear late Saturday: 
 
 _Officials decided to reduce rising pressure inside the reactor vessel, so they vented some of the steam buildup. They needed to do that to prevent the entire structure from exploding, and thus starting down the road to a meltdown. 
 
 _At the same time, in order to keep the reactor fuel cool, and also prevent a meltdown, operators needed to keep circulating more and more cool water on the fuel rods. 
 
 _Temperature in the reactor vessel apparently kept rising, heating the zirconium cladding that makes up the fuel rod casings. Once the zirconium reached 2,200 degrees Fahrenheit (1,200 Celsius), it reacted with the water, becoming zirconium oxide and hydrogen. 
 
 _When the hydrogen-filled steam was vented from the reactor vessel, the hydrogen reacted with oxygen, either in the air or water outside the vessel, and exploded. 
 
 A similar "hydrogen bubble" had concerned officials at the 1979 Three Mile Island nuclear disaster in Pennsylvania until it dissipated. 
 
 If the temperature inside the Fukushima reactor vessel continued to rise even more _ to roughly 4,000 degrees Fahrenheit (2,200 Celsius) _ then the uranium fuel pellets would start to melt. 
 
 According to experts interviewed by The Associated Press, any melted fuel would eat through the bottom of the reactor vessel. Next, it would eat through the floor of the already-damaged containment building. At that point, the uranium and dangerous byproducts would start escaping into the environment. 
 
 At some point in the process, the walls of the reactor vessel _ 6 inches (15 centimeters) of stainless steel _ would melt into a lava-like pile, slump into any remaining water on the floor, and potentially cause an explosion much bigger than the one caused by the hydrogen. Such an explosion would enhance the spread of radioactive contaminants. 
 
 If the reactor core became exposed to the external environment, officials would likely began pouring cement and sand over the entire facility, as was done at the 1986 Chernobyl nuclear accident in the Ukraine, Peter Bradford, a former commissioner of the U.S. Nuclear Regulatory Commission, said in a briefing for reporters. 
 
 Another expert on the call, Ken Bergeron, a physicist and former Sandia scientist, added that as a result of such a meltdown the surrounding land would be off-limits for a considerable period of time, and "a lot of first responders would die." 
 
 ___ 
 
 AP National Writer Jeff Donn reported from Boston. ||||| 2.40am: Good morning. It's now more than three days since the earthquake and tsunami hit Japan, but there is little sign of relief for survivors. 
 
 • There has been a second blast at the Fukushima No 1 nuclear plant. Television footage suggests the outer building of the third reactor has been blown away – as in the first blast – but officials believe the reactor container remains intact and says there is little prospect of a significant release of radioactive material. Officials warned yesterday that there might be another hydrogen explosion. 
 
 • The Daily Yomiuri newspaper says police are reporting about 1,000 bodies have been found in Minamisanriku, Miyagi and another 1,000 on the Ojika Peninsula coast in the prefecture. 
 
 • A very alarming tsunami warning this morning now appears to be a false alarm. Sirens along the coast sounded and television and radio alerts said officials had warned of a wave up to three metres high. The Japanese meteorological agency is now saying they believe it to be a false alarm and that there was no sign of a quake large enough to trigger a tsunami, although broadcaster NHK is apparently reporting that a helicopter pilot observed a large incoming wave. 
 
 The Guardian's Dan Chung and Jonathan Watts are reporting from the disaster zone. Their video on the aftermath near Sendai in Miyagi prefecture is here 
 
 2.50am: Japanese television earlier reported that the sea level had dropped five metres off the coast of Fukushima. The feeling in Japan is already tense following an earlier aftershock this morning, and much fear spreading across the country after unconfirmed reports of another tsunami. The Japanese Meteorological Agency says that no tsunami is expected. 
 
 3.00am: Japan's chief cabinet secretary, Yukio Edano, says a hydrogen explosion has occurred at Unit 3 of Japan's stricken Fukushima Daiichi nuclear plant. The blast was similar to an earlier one at a different unit of the facility. 
 
 People within a 12 mile radius have been ordered inside. Reports in the area say they felt the explosion 30 miles away, according to AP. 
 
 The No. 3 Unit reactor had been under emergency watch for a possible explosion as pressure built up there following a hydrogen blast Saturday in the facility's Unit 1. 
 
 More than 180,000 people have evacuated the area. 
 
 3.12am: It has now been confirmed that the reactor's inner containment vessel holding nuclear rods is intact. 
 
 TOKYO (AP) Tokyo Electric Power Co. says 3 injured, 7 missing after explosion at Japan nuclear plant. 
 
 3.45am: Chief cabinet secretary Yukio Edano has told reporters that the reactor unit appears intact and that the pressure inside the reactor has stabilised. 
 
 "I believe people who have seen the images are anxious about the situation, [but] according to the data we have been able to obtain, the containment vessel is not damaged," he added. 
 
 3.54am: More from Edano: plans to impose rolling black-outs in parts of Tokyo and the surrounding area are on hold for now. Tokyo Electric Power is asking everyone to try to limit electricity use, but will go ahead with the power cuts if that does not prove sufficient. The closure of nuclear plants has led to a drastic shortfall in supply. 
 
 But Japan's Jiji news agency says neighbouring Tohoku Electric Power is now considering black-outs. 
 
 AP reports that rail operators have suspended or reduced many regional services to try to reduce the demand for power. 
 
 3.59am: Justin McCurry, the Guardian's correspondent in Japan' has sent this message about the mood there this morning, following the tsunami warning and second explosion at the Fukushima nuclear plant. 
 
 "The general feeling is that the danger from quakes, tsunami and radiation leaks is far from over. News of the blast came as the Nikkei stock average lost more than 4.5% in morning trading and the Bank of Japan pumped 15 trillion yen of liquidity into the financial system. There are reports of panic buying in Tokyo of items such as batteries, instant noodles and water. There is no visible exodus, but plenty of anecdotal evidence of people, particularly expatriates, leaving the Tokyo area and heading to western Japan or overseas. The combination of a large aftershock this morning, rolling power cuts, the nuclear crisis in Fukushima and another tsunami alert - which proved to be a false alarm - has set nerves jangling across the region." 
 
 Justin has written a fuller piece on the mood in Japan, which you can read here 
 
 4.07am: Six workers were injured in the explosion at the Fukushima power plant, but all are conscious, NHK reports. 
 
 4.26am: Kyodo is reporting that many shops and manufacturers have closed in Tokyo and the surrounding area due to the power rationing. Sony has closed a facility producing industrial adhesive tape while Toshiba has suspended operations at a factory producing goods such as flat screen TCs. Other companies – such as Toyota - had already suspended operations because of their production is in the north east. 
 
 Isetan Mitsukoshi has closed all seven of its department stores in the region around the capital and Odakyu Department Store Compay and Sogo & Seibu each closed three branches. 
 
 An NHK twitter feed (@nhk_asianvoices) says the government has text-messaged citizens urging a nationwide effort to save energy. 
 
 4.45am (1.45pm JST) IEEE Spectrum has an interesting piece here on the role that rescue robots will play in operations. Unsurprisingly Japan has a lot of expertise of its own, but as their teams are deployed already the piece cites Dr Robin Murphy, director of the Center for Robot-Assisted Search and Rescue at Texas A&M University. 
 
 Dr. Murphy, an IEEE Fellow whose team has taken robots to disaster sites like the World Trade Center after the September 11, 2001 attacks and New Orleans after hurricane Katrina, tells me that robots have been used in at least one previous earthquake, the 2010 Haiti disaster. The U.S. Army Corps of Engineers, she says, used a Seabotix underwater remotely operated vehicle, or ROV, to investigate bridge and seawall damage as part of the U.S. assistance to the Haitian government. For a disaster like the Japan quake, she says several types of robots could prove useful, including: • small unmanned aerial vehicles like robotic helicopters and quadrotors for inspection of upper levels of buildings and lower altitude checks; • snake robots capable of entering collapsed buildings and slithering through rubble; • small underwater ROVs for bridge inspection and underwater recovery; • tether-based unmanned ground vehicles like sensor-packed wheeled robots that operators can drive remotely to search for survivors. 
 
 Incidentally, if you're wondering why the time stamp has got longer, reader gaikokujin used the comments section to request we add Japanese times - we will do so from now on; thanks for the suggestion. 
 
 4.52am (1.52pm JST): According to this piece in the New York Times, a US aircraft carrier, Ronald Reagan, which is sailing in the Pacific, passed through a radioactive cloud from the Japan nuclear reactors. It is reported that the crew on deck received a month's worth of radiation in an hour. 
 
 There is no indication any of the personnel have experienced ill effects from the exposure, officials said. 
 
 5.15am (2.15pm JST): Tokyo Electric Power Company, which runs the Fukushima Daiichi plant, says radiation levels at the unit are well below the legal limits following this morning's hydrogen explosion. Radiation at Unit 3 measured 10.65 microsieverts; operators must inform the government if a level of 500 microsieverts is reached. 
 
 Health experts have stressed that the risk from radiation appears low. Reuters has spoken to the Gregory Hartl of the World Health Organisation, who told the agency: 
 
 
 
 "At this moment it appears to be the case that the public health risk is probably quite low. We understand radiation that has escaped from the plant is very small in amount." 
 
 That has not stopped people from worrying. Singaporean authorities have announced they will test imported Japanese produce for potential radiation "as a precautionary measure". 
 
 
 
 5.38am (2.38pm JST): This screen grab, taken from NHK, shows the Fukushima No 1 nuclear plant before and after this morning's blast. 
 
 Officials say it was similar to the earlier hydrogen explosion; The Guardian's Ian Sample has put together this Q&A to explain how that happened. 
 
 5.53am (2.53pm JST): Some links that may be useful if you or someone you know is near the disaster zone: @dailyyomiuri has tweeted links for information on English-speaking doctors and hospitals in Iwate, visit http://tinyurl.com/IwateHospitals and Fukushima - though clearly some of these services are likely to have been affected themselves. 
 
 This Google map (Japanese only) shows meal and water supplies, evacuation spots and places to charge cellphone batteries 
 
 If you're in Tokyo and trying to cut your electricity consumption, this is a guide to how much power appliances use. 
 
 6.02am (3pm JST): An update on the situation at Fukushima's second nuclear plant (ie not the one that experienced the blast this morning) from the UN nuclear watchdog, released at 4.15am GMT (1.15pm JST). 
 
 The International Atomic Energy Agency reported: 
 
 Based on information provided by Japanese authorities, the IAEA can confirm the following information about the status of Units 1, 2, 3 and 4 at Fukushima Daini nuclear power plant. All four units automatically shut down on March 11. All units have off-site power and water levels in all units are stable. Though preparations have been made to do so, there has been no venting to control pressure at any of the plant's units. At unit 1, plant operators were able to restore a residual heat remover system, which is now being used to cool the reactor. Work is in progress to achieve a cold shutdown of the reactor. Workers at units 2 and 4 are working to restore residual heat removal systems. Unit 3 is in a safe, cold shutdown. Radiation dose rate measurements observed at four locations around the plant's perimeter over a 16-hour period on 13 March were all normal. 
 
 6.09am (3.09pm): The Guardian's Japan correspondent Justin McCurry has more information on the financial and economic impact of the disaster: 
 
 Japanese shares were heading for huge losses on Monday after the fallout from last week's deadly tsunami sent the Nikkei stock average down by more than 6% in Tokyo. Monday was the first full day of trading since the earthquake and tsunami brought devastation to vast parts of Japan's northeast coast. The scale of the damage is expected to exact a heavy economic toll and force the government to borrow heavily to fund the rebuilding effort. Concern is also mounting about the disaster's impact on energy supplies in the wake of serious problems with reactors at two quake-damaged atomic power plants. The yen slid against the dollar after the Bank of Japan said it would pump a total of 15 trillion yen into the financial system to ensure liquidity for private lenders affected by the quake. The bank will inject a further 3 trillion yen on Wednesday. Japan's automakers, electronics firms and oil refiners were among the hardest hit in Monday's trading, and saw their share prices drop by double-digit percentages. Toyota, the world's biggest carmaker, said it would suspend all production in Japan until at least Wednesday. Nissan and Honda have announced similar measures. The broader TOPIX index fell 7.6% and was on course for its biggest single-day loss since October 2008, when stocks nosedived after the Lehman shock. Japan's central bank, which is holding a policy meeting on Monday, said it would closely monitor currency markets. Some analysts expected the bank to announce further emergency measures later in the day. 
 
 6.19am (3.19pm JST): China is willing to offer more help to Japan, Premier Wen Jiabao said today in his annual press conference. A rescue team arrived yesterday and Beijing has also sent relief supplies. Reuters reports: 
 
 China has set aside acrimony over territorial disputes and wartime memories to extend the hand of friendship to Japan, sending a team of rescuers to help search for survivors from the disaster, which likely killed more than 10,000 people. "I want to use today's opportunity to extend our deep condolences for the loss of lives in this disaster and to express our sincere sympathy to the Japanese people," Wen said. "China is also a country that is prone to earthquake disasters and we fully empathise with how the Japanese people feel now," he added. "When the massive Wenchuan earthquake hit the Japanese government sent a rescue team to China and also offered supplies," said Wen, referring to the 2008 Sichuan earthquake that killed more than 80,000 people. "We will continue to provide further necessary aid to Japan in accordance with their needs." 
 
 7.25am (4.25pm JST): If you've just joined us, a quick summary of the situation this morning: 
 
 • The nuclear crisis at Fukushima No 1 nuclear plant continues, with a hydrogen explosion blowing off a reactor building and injuring 11 people. 
 
 The blast at the number 3 reactor had been anticipated and was similar to the explosion seen previously at the number 1 reactor. It has not, apparently, damaged the reactor itself or the containment vessel and authorities said radiation levels were normal around it. 
 
 However, Japanese media are reporting that cooling has now failed at a third reactor at the plant (confusingly, number 2 reactor). 
 
 • Police are reporting that about 1,000 bodies have been found in Minamisanriku and another 1,000 on the Ojika Peninsula coast in Miyagi, the worst hit prefecture, according to Japanese media. 
 
 • Plans for rolling black outs in Tokyo and the surrounding area are currently suspended. Many private firms have voluntarily halted business or taken other measures to help reduce demand; although supply has been hit badly by the nuclear plant closures, it is still keeping up with consumption at present. 
 
 • An early morning tsunami alert, with sirens and broadcast warnings, turned out to be a false alarm. But authorities have warned people to remain careful as aftershocks of up to 6.2 magnitude continue to rock the north east. 
 
 • Japan has said it may deploy reservists to supplement the 100,000 troops working on rescue and relief operations, NHK reports. If so, it would be the first time they had ever been required to cope with a natural disaster. 
 
 • Shares fell sharply and the yen slid against the dollar as financial markets reopened this morning. 
 
 More powerful footage is emerging of the disaster. This six minute video of the tsunami striking a town is thought to have been shot in Kesennumma, Miyagi, which we know from earlier reports was devastated by the waves. 
 
 7.40am (4.40pm JST): A UK International Search and Rescue (Isar) team is due to join an international hunt for survivors in the city of Ofunato, about 100 miles north of Sendai on the east coast. 
 
 The group, organised by the Department for International Development, is made up of 63 UK fire service search and rescue specialists, two rescue dogs and a medical support team. 
 
 The experts arrived in Japan yesterday on board a private charter plane carrying 11 tonnes of specialist rescue equipment, including heavy lifting and cutting gear. 
 
 Roy Wilshire, the team's leader, said it had met members of the US military and was travelling in convoy to Ofunato, which has a population of around 42,000. 
 
 "There are apparently hundreds of people missing there and we are in a convoy of several hundred rescuers,'' he told the BBC. 
 
 "When we arrive we will set up our base before taking instruction from members of the Japanese fire and rescue service." 
 
 7.58am (4.58pm JST): Associated Press has a disturbing report on the conditions for survivors despite a massive relief operation. 
 
 "People are surviving on little food and water. Things are simply not coming," said Hajime Sato, a government official in Iwate prefecture, one of the three hardest hit. "We have repeatedly asked the government to help us, but the government is overwhelmed by the scale of damage and enormous demand for food and water," he told The Associated Press. "We are only getting around just 10 percent of what we have requested. But we are patient because everyone in the quake-hit areas is suffering." He said local authorities were also running out of body bags and coffins. "We have requested funeral homes across the nation to send us many body bags and coffins. But we simply don't have enough. We just did not expect such a thing to happen. It's just overwhelming." 
 
 A second account focuses on the desperate situation at a hospital in Takajo, Miyagi: 
 
 
 
 The nurses have been cutting open soiled intravenous packs and scrubbing down muddy packs of pills with alcohol to cleanse them... "I'm sorry, we have no medicine," the staff repeatedly told a constant flow of people from the town, many of them elderly. 
 
 8.15am (5.15pm JST): A quick clarification: mjhollamby has pointed out (in the comments) that the UN's nuclear watchdog said six workers were injured in this morning's blast. However, the government revised the numbers upwards after the IAEA produced their statement. 
 
 According to Reuters, Yukio Edano - the chief government spokesman - said four personnel from the Self Defence Force and seven power plant workers were injured. One of the workers was seriously injured but remains conscious; the troops were only slightly injured and have already returned to work. 
 
 8.36am (5.36pm JST): This map created by Chris A is being shared a lot on Twitter. It purports to show the location of Japan's nuclear power facilities (although there are 55 nuclear power plants in the country, they are spread over 17 sites, according to the website of the Federation of Electric Power Companies of Japan). 
 
 
 
 View Nuclear Power facilities of Japan in a larger map 
 
 The exclamation mark (which become marks if you zoom in close enough) show the site of the two meltdowns. Thanks to @garethoconnor on Twitter for the link. 
 
 This is Adam Gabbatt taking over from Tania and Lee. 
 
 8.48am (5.48pm JST): My colleague Peter Walker writes that Japan's Research Laboratory for Nuclear Reactors is still insisting that there is no cause to fear a major nuclear accident. 
 
 An expert from the body told NHK TV's English-language service that while it was possible there would be similar explosions in the No 2 and No 4 reactor buildings at the Fukushima plant, all important safety features remained intact and plans to cool the reactors with seawater should be effective. 
 
 9.15am (6.15pm JST): Confusing reports regarding the Fukushima Daiichi plant. According to some sources Tokyo Electric Power Company (Tepco), which runs the plant, has declared that the No 1 and 2 reactors are out of emergency. 
 
 Other reports this morning suggested that the No 2 reactor had actually suffered a loss of its cooling function, with water levels at the reactor dropping. Government officials said efforts were under way at the No 2 reactor to prevent what would be the plant's third explosion since Saturday. 
 
 9.36am (6.36pm JST): A quick note from my colleague James Randerson on the "Richter Scale" – the logarithmic magnitude scale that was defined in 1935 to measure earthquakes in California. It was developed by Charles 
 
 Richter (who also happened to be a nudist) and Beno Gutenberg of the California Institute of Technology (CIT) and was originally referred to as "Local Magnitude" or ML, James writes: 
 
 Even though it was superseded in 1979 by the more uniformly applicable moment magnitude (Mw) scale the Richter scale has an amazing staying power in the public, and it has to be said journalistic, mind. In the barrage of information about the Japan earthquake numerous articles have used to the old scale incorrectly (including on occasion ours). 
 
 Scientists no longer use Richter's original methodology as it does not work for large quakes or ones where the epicentre is greater than 600km away. Science writer Ted Nield explains in this amusing piece from 2007 on the scale's staying power: 
 
 New magnitude scales that extended Richter and Gutenberg's original idea were developed as the number of recording stations worldwide increased. These include body-wave magnitude (Mb) and surface wave magnitude (Ms). Each is valid over a particular range of frequency and type of signal, and within its own parameters is equivalent to "Richter" magnitude. But because of the limitations of all three (especially the tendency to become saturated at high magnitudes, so that very large events cannot be easily distinguished) a more uniformly applicable magnitude scale, known as moment magnitude (Mw), was developed in 1979 by two other CIT scientists, Tom Hanks and Hiroo Kanamori. For very large earthquakes, Mw gives the most reliable estimate of earthquake size, and this is the measure that is always misreported as "the Richter Scale". 
 
 10.02am (7.02pm JST): The No 2 reactor at the Fukushima Dai-Ichi plant has lost all its cooling capacity, according to Japan's Nuclear and Industrial Safety Agency. 
 
 NHK World is reporting that Tokyo Electric Power Company, which owns the plant, has notified the agency of an emergency at the No 2 reactor. 
 
 This is the second emergency notice for the reactor. The utility firm told the agency shortly after the quake on Friday that the reactor's emergency cooling power system had failed. Since then, the company tried to cool the reactor by circulating water by steam power, instead of electricity. But an attempt to lower the temperature inside the vessel that houses the reactor did not work well. Fears of a hydrogen explosion at the vessel housing building are growing as the water level of the reactor is falling. A reaction with the steam and exposed fuel rods generates a large amount of hydrogen. 
 
 10.18am (7.18pm JST): The Australian broadcaster ABC has posted a series of before and after satellite images from around north east Japan which give a clear sense of how much devastation the tsunami caused. The viewer can slide back and forth between the before and after shots, seeing how entire towns have been swept away. See the gallery here. 
 
 10.27am (7.27pm JST): Water levels have fallen far enough to partly expose fuel rods at the No 2 reactor at Fukushima Daiichi, according to the Jiji news agency. 
 
 10.37am (7.37pm JST): Below the line Hoxtoner, who is in Japan, writes: 
 
 Just went to the local supermarket here in Sendai. NOTHING !! You have to see it to believe it. The only things I saw that were in bulk was alcohol, fags, coffee and tea and there wasn't much of that. Other nationalities have been instructed to leave the Tohoku area. I have checked the British FCO and I don't see any such statement. The Electric came on here in the early hours on Sat. We have water,but no gas. It's also a bad hayfever day to add on to all the tragedies and anxieties. I don't usually drink during the day yet I've decided to pour myself out a beer. Slight aftershocks and helicopters flying around as I type. 
 
 10.50am (7.50pm JST): The Guardian's science correspondent, Ian Sample, writes that the first report from Japan's Nuclear and Industrial Safety Agency this morning described a rise in radioactivity around the Fukushima nuclear power station when compared to Sunday's levels. 
 
 The highest level, at 680microSieverts per hour, was measured earlier on Monday in a direction north-northwest of the plant, the wind direction at the time. To put that level in perspective, the typical dose we receive from background radiation is 2000 microSieverts a year. So spending an hour at the monitoring post leads to an exposure equivalent to around four months due to background. The Nuclear and Industrial Safety Agency report that at 1.10am local time on Monday, engineers had to stop pumping water into reactors one and three at Fukushima because seawater pits ran dry. Injection of water in the reactor 3 - the one that uses a plutonium mix fuel - restarted at 3.20am. They give no further details of the situation at reactor 1. 
 
 10.56am (7.56pm JST): The Guardian has posted this gallery of images from Japan. 
 
 11.03am (8.03pm JST): Kyodo News has reported in the last five minutes that the fuel rods at the No 2 reactor at Fukushima Daiichi are now fully exposed. 
 
 11.09am (8.09pm JST): Ian Sample has more on the exposure of those fuel rods at reactor 2: 
 
 The rods are usually submerged in several metres of water to stop them overheating. Water level gauges at reactors 1 and 3 also suggest that fuel rods are partially exposed, but engineers said pressure readings from the reactors conflict with this and that the water gauges may be faulty. Workers are trying to circulate seawater around all three reactors to keep them cool. Serious melting of fuel rods inside any of the reactors could block the circulation of water. 
 
 11.20am (8.20pm JST): This dramatic amateur footage, shot in various locations around north-east Japan, shows raging tsunami waves rushing over embankments and flowing into cities and towns carrying vehicles, ships and houses inland. 
 
 . 
 
 11.26am (8.26pm JST): The International Atomic Energy Authority website appears to have suffered amid a surge in traffic, Ian Sample has just told me. Ian says their back-up system is working fine though: you can find all their announcements on the Japanese nuclear crisis on their Facebook page. 
 
 11.38am: The Guardian will be staging a live Q&A with nuclear experts from 1pm, inviting readers to post their questions about the events at Fukushima Daiichi to a panel of scientists. 
 
 You can post your questions in advance here, and I'll link again to the Q&A when it starts. 
 
 11.48am: The Swiss government has suspended plans to replace and build new nuclear plants, pending a review of two hydrogen explosions at Japanese plants. 
 
 AP reported that the suspension affects three requests for "blanket authorization for nuclear replacement until safety standards have been carefully reviewed and if necessary adapted." 
 
 The government is considering applications for a new plant in Solothurn and replacement plants in Aargau and Bern. 
 
 The head of the Swiss federal energy department, Doris Leuthard, said she has decided to suspend the plans because "safety has absolute priority." She says she has instructed the government to study what caused the Japanese explosions in the wake of Friday's massive earthquake and tsunami. 
 
 11.57am: A press briefing in the UK, aimed at promoting the benefits of nuclear power and due to take place tomorrow, has been postponed "because it would be inappropriate given the events in Japan". 
 
 Sir David King, Director of the Smith School of Enterprise and the Environment at Oxford University, had been due to present a report entitled 'A low carbon nuclear future: Economic assessment of nuclear materials and spent nuclear fuel management in the UK', and argue the need to develop a new long term strategic nuclear plan which encompasses new build and legacy issues. 
 
 12.17pm: Radioactive steam could continue to be released from reactors at Fukushima Daiichi for "weeks or even months", the New York Times is reporting. 
 
 The newspaper says reactor operators "now have little choice but to periodically release radioactive steam as part of an emergency cooling process for the fuel of the stricken reactors that may continue for a year or more even after fission has stopped". 
 
 The plant's operator must constantly try to flood the reactors with seawater, then release the resulting radioactive steam into the atmosphere, several experts familiar with the design of the Daiichi facility said. That suggests that the tens of thousands of people who have been evacuated may not be able to return to their homes for a considerable period, and that shifts in the wind could blow radioactive materials toward Japanese cities rather than out to sea. Re-establishing normal cooling of the reactors would require restoring electric power — which was cut in the earthquake and tsunami — and now may require plant technicians working in areas that have become highly contaminated with radioactivity. 
 
 The newspaper quoted a senior nuclear expert in Japan as saying "under the best scenarios, this isn't going to end anytime soon". 
 
 The New York Times also has this excellent interactive explaining how a reactor shuts down. 
 
 12.28pm: NHK World reports that "a core meltdown might have occurred" at reactor 2, Fukushima Daiichi. 
 
 The Nuclear and Industrial Safety Agency has tried to circulate the coolant by steam instead of electricity, but NHK reported that attempts to lower the temperature inside the reactor chamber have not worked well. 
 
 NISA is reportedly also considering opening a hole in the reactor housing building to release hydrogen generated by the exposed fuel rods. 
 
 12.36pm: My colleague Luke Harding is live blogging from the Hamburg offices of Der Spiegel as part of the Guardian's New Europe season, and reports that the German news magazine has decided to pull its reporter out of Tokyo because of the risk of a Chernobyl-style radiation cloud reaching the Japanese capital. 
 
 Thilo Thielke, Spiegel's veteran war correspondent, is leaving Japan today. Spiegel is now covering the story from Bangkok and the south of Japan. Mathias Müller von Blumencron says the latest information is ominous: the wind is blowing to the south – in the direction of Tokyo. "Perhaps this is a piece of German angst. But no country is more against nuclear power than Germany," he says. He adds: "The wind is shifting from the north and could blow a cloud south directly to Tokyo. This is really horrible. I think this is a big, big crisis and a wake-up call for nuclear energy." The German embassy is also making preparations to evacuate some staff, apparently. 
 
 12.57pm: Hello, this is Haroon Siddique, taking over for a while to give Adam a break. Our Berlin correspondent Helen Pidd has sent an interesting update relating to steps being taken in Germany concerning the country's nuclear programme in response to events in Japan: 
 
 Germany's chancellor Angela Merkel is expected to announce the suspension of plans to extend the life of its nuclear power stations later today. In the light of the Japanese disaster, Merkel has decided to re-examine her highly controversial decision last year to renew Germany's nuclear plants, the German media is reporting. Government sources have told FOCUS online that Merkel took the decision on Sunday night after a crisis meeting at the Berlin headquarters of her Christian Democratic Union (CDU) party. She is expected to confirm the suspension today at press conference at 4pm local time (3pm GMT) with her foreign minister, Guido Westerwelle. 
 
 1pm: There have been 38 earthquakes in or around Japan today alone, according to the US geological survey. The most powerful recorded today so far was 6.1 in magnitude. 
 
 1.35pm: Here's a summary of events so far today: 
 
 • A "core meltdown" might have occurred at reactor 2 Fukushima Daiichi. NHK World reports, as fears grow over the safety of the nuclear plant continues. Fuel rods are reportedly fully exposed. The nuclear and industrial safety agency (NISA) has tried to circulate the coolant by steam instead of electricity, but NHK reported that attempts to lower the temperature inside the reactor chamber have not worked well. NISA is reportedly also considering opening a hole in the reactor housing building to release hydrogen generated by the exposed fuel rods. 
 
 • A hydrogen explosion at the number 3 reactor at the Fukushima No 1 nuclear injured 11 people. The blast had been anticipated and was similar to the explosion seen previously at the number 1 reactor. It has not, apparently, damaged the reactor itself or the containment vessel and authorities said radiation levels were normal around it. 
 
 • Police are reporting that about 1,000 bodies have been found in Minamisanriku and another 1,000 on the Ojika Peninsula coast in Miyagi. Miyagi has been the worst hit prefecture. Video footage is continuing to emerge revealing the force of the tsunami that swept into north east Japan. 
 
 • Plans for rolling black outs in Tokyo and the surrounding area are currently suspended. Many private firms have voluntarily halted business or taken other measures to help reduce demand; although supply has been hit badly by the nuclear plant closures, it is still keeping up with consumption at present. 
 
 Other countries have been reviewing their nuclear programmes in the light of events in Japan. Switzerland has suspended plans to replace and build new nuclear plants and Germany is expected to is expected to announce the suspension of plans to extend the life of its nuclear power stations later today. ||||| 1.30pm (10.30pm JST): Good afternoon, welcome to the Guardian's live coverage of the Japanese humanitarian crisis and latest updates on conditions at the Fukushima Daiichi nuclear power plant. Here's a summary of the days events so far: 
 
 • Authorities are struggling to control the situation at the Fukushima Daiichi nuclear plant, where the situation in reactors No 3 and No 4 remains fast-moving and perilous. 
 
 Reactor 3 is a particular worry – Japan's government said today that there a "possibility" that the reactor's primary containment vessel for radiation had been damaged after steam was seen rising into the air. Attempts to drop water from helicopters was abandoned due to radiation levels. The latest mooted plan involves a police water cannon truck. 
 
 Staff dousing reactors with seawater were forced to evacuate part of the building for a period this morning after radiation levels surged. These later receded and staff returned. 
 
 French government ministers have urged the country's nationals in Tokyo to leave Japan or else head south in case radiation is blown onto the capital, saying Japanese authorities had "visibly lost control". 
 
 • The country faces an increasingly desperate humanitarian crisis caused by the direct effects of Friday's huge earthquake and resultant tsunami, one made worse by freezing weather. 
 
 The official death toll has now hit 4,255 deaths, with 8,194 people registered as unaccounted for. Survivors, many of them homeless, are struggling with a wave of cold weather forecast to last well into this week, with night time temperatures dipping to -5C in some places. 
 
 • Japan's emperor, Akihito, has made a rare TV appearance to express his condolences to his people and his worry at the nuclear situation. 
 
 
 
 • Following its precipitous plunge yesterday, Tokyo's stock market bounced back nearly 6%. Japan's central bank has injected a further $40bn into the financial markets. 
 
 You can read our previous live blog following Wednesday's developments here. 
 
 1.41pm (10.41pm JST: Ian Sample, the Guardian's science correspondent, has been talking to Andrew Sherry, director of the Dalton Nuclear Institute at Manchester University, about steam seen rising from the reactor 3. Ian says the fact steam is escaping does not necessarily mean any of the "serious containment structures" within reactor 3 have been damaged: 
 
 Specifically, I wondered how the steam could be radioactive, given all the containment systems that surround the reactor core. This is different to the steam that is released regularly when the engineers vent the pressure vessel after pumping it full of seawater. One likely scenario is this: high pressures in the reactor vessel can cause it to dump steam into what's called a torus beneath it. This is a metal donut half-filled with water. That torus was thought to be damaged in yesterday's explosion, so steam might be leaking from that. Crucially, the torus is outside any of the serious containment structures - only the outer building can hold the radioactive steam in, but the outer building was torn apart in an explosion. Another source of the steam is water boiling at the spent fuel rod pools. 
 
 1.46pm (10.46pm JST: My colleague Martin Shuttleworth has updated the Guardian's before and after pictures showing the devastation caused by the Japanese tsunami. 
 
 The images show a lot of is yet to recede from the worst hit areas. 
 
 1.58pm (10.58pm JST): James Randerson has sent through some more interesting nuclear context, from the UK's Institution of Mechanical Engineers. He particularly highlights this snippet: 
 
 A concern for the people not just of Japan but the Pan Pacific area is whether Fukushima will turn into the next Chernobyl with radiation spread over a big area. The answer is that this scenario is highly unlikely, because of the wildly different design of the two reactors. 
 
 The reason why radiation was disseminated so widely from Chernobyl with such devastating effects was a carbon fire. Some 1,200 tonnes of carbon were in the reactor at Chernobyl and this caused the fire which projected radioactive material up into the upper atmosphere causing it to be carried across most of Europe. 
 
 There is no carbon in the reactors at Fukushima, and this means that even if a large amount of radioactive material were to leak from the plant, it would only affect the local area. 
 
 The Japanese authorities acted swiftly and decisively in evacuating people living within 20km of the plant, and ensuring people living within 30km of the plant remained in their homes, with windows and doors closed. The radiation measured so far at Fukushima is 100,000 times less than that at Chernobyl. 
 
 2.23pm (11.23pm JST): The New York Times has gone big today on comments by Yukio Edano, variously described as the chief cabinet secretary or the government's chief spokesman, that a cloud of steam rising from the No 3 reactor at the Fukushima nuclear plant indicated that the reactor's containment vessel, designed to keep in radiation, might have been ruptured. At a subsequent press conference he said that there was little chance of serious damage. But as the NYT notes, the "rapid and at times confusing pronouncements" by Japan's government are far from reassuring. 
 
 2.31pm (11.31pm JST): It seems that a small number of people are benefiting from the nuclear scare: Adam Gabbatt reports here how sales of potassium iodide supplements, intended to limit the risk from radiation, have soared in the US and Canada. 
 
 2.45pm (11.45pm BST): A man from the University of Canterbury in New Zealand who put together an interactive map of the various tremors which hit Christchurch has done the same for Japan (see screengrab below). It's fascinating – and frightening – to watch the sheer number of aftershocks. 
 
 - 
 
 2.51pm (11.51pm JST): The main focus on this new blog so far has been on the nuclear situation, which is in some ways understandable as it's the most fast-moving and unpredictable element of the story, four days after the main quake and tsunami. But it's worth reiterating – as I tried to in this morning's blog – that a far greater humanitarian crisis remains. 
 
 As well as an official death toll now over 4,200, which will inevitably rise much higher, hundreds of thousands of people have been left homeless, in many cases losing just about every possession. Their plight has been made worse by the severe weather affecting much of Japan's north-east at the moment, with some areas experiencing blizzards and temperatures of -5C. There are temporary evacuation shelters but these are generally basic and often very chilly. Food and fuel are in short supply. 
 
 As we reach midnight in Japan it's perhaps worth looking through today's photo gallery of the quake aftermath and reflecting that worries about Chernobyl-style clouds of radioactivity sweeping across the Pacific, while understandable, are not the only issue. 
 
 3.20pm (12.20am JST): John Vidal reports that David Cameron has said nuclear power should remain part of the UK's energy mix, while stressing there were lessons to be learned from the Japanese nuclear crisis. 
 
 "I do think that nuclear power should be part of the mix in future as it is part of the mix right now," Cameron told parliament. 
 
 "Obviously I'm sure that everyone watching the dreadful events in Japan will want to make sure we learn any lessons." 
 
 Cameron's comments have provoked an immediate response from environment groups, John says. Here's a statement from Friends of the Earth: 
 
 The events in Japan must lead to an urgent review of UK plans to build more nuclear reactors. The UK can meet its energy needs and tackle climate change by harnessing its vast renewable energy potential and slashing energy waste – new nuclear stations will inevitably starve these programmes of vital funds. We must invest in a cleaner, safer future – nuclear power is a gamble we don't need to take. 
 
 3.34pm (12.34am JST): Japanese authorities have "reported concerns" about the condition of the spent nuclear fuel pool at Fukushima Daiichi Unit 3 and Unit 4, the International Atomic Energy Agency has said. 
 
 Japanese Defence Minister Toshimi Kitazawa announced Wednesday that Special Defence Forces helicopters planned to drop water onto Unit 3, and officials are also preparing to spray water into Unit 4 from ground positions, and possibly later into Unit 3. Some debris on the ground from the 14 March explosion at Unit 3 may need to be removed before the spraying can begin. 
 
 The IAEA quote above is already a little out of date – while Japan had indeed planned to use helicopters, we heard earlier that this plan had to be abandoned due to radiation levels. 
 
 With the helicopters abandoned, plans are apparently now reliant on water cannon being deployed from ground level. 
 
 3.44pm (12.44am JST): Right on cue, Kyodo news is reporting that a "water cannon vehicle" has arrived at reactor 4. 
 
 3.49pm (12.49am JST): Suzy Goldenberg has just been on a conference call with US energy secretary and Nobel prize winner (in atomic physics) Stephen Chu. Suzy was tweeting as Chu spoke – here's a sample: 
 
 • @suzyji Chu - There are several reactors now at risk. We do not want to speculate as to what will happen #eg 
 
 • @suzyji Chu - We think there is a partial meltdown in #Japan, but doesn't mean containment vessel will fail #eg 
 
 3.55pm (12.55am JST): Reuters is reporting that the head of the International Atomic Energy Agency has said the situation at the Fukushima Daiichi nuclear power plant is "very serious". 
 
 4.03pm (1.03am JST): "The magnitude of the Japanese earthquakes and the main resulting tsunami are apparent from the immense scale of devastation and from the fact that all countries around the Pacific were affected," says Dr Philippe Blondel, deputy director of the Centre for Space, Atmospheric & Oceanic Science at University of Bath. 
 
 Blondel adds that the "current fears about nuclear safety should not shadow the huge plight of the refugees": 
 
 For example, the tsunami waves were still more than 1m high when they reached New Zealand, having travelled the 8,000 km in about 12 hours. And they even reached Antarctica, albeit much reduced in height. The current fears about nuclear safety should not shadow the huge plight of the refugees and the difficulties of on-going search and rescue operations. They are taking place in the background of regular earthquakes, some of them associated to tsunami alerts. The Japanese Meteorological Agency estimated on Monday that the next 3 days would see a 40% probability of large aftershocks (more than magnitude 5), reducing to 20% from 17-20 March. Current activity supports their predictions." 
 
 4.13pm (1.13am JST): The US is to fly a spy plane over the stricken Fukushima plant in a bid to get a closer look at the damage, according to Kyodo news. 
 
 The Japanese news agency said the military will operate an unmanned Global Hawk high-altitude reconnaissance aircraft over the plant, perhaps as soon as Thursday, to examine the plant's reactors, Kyodo said, quoting a government source. 
 
 "Photographs taken by the plane equipped with infrared sensors could provide a useful clue to what is occurring inside the reactor buildings, around which high-level radiation has been detected," it added. 
 
 4.21pm (1.21am JST): The director general of the International Atomic Energy Agency, Yukiya Amano, has said he will travel to Japan as soon as possible, perhaps arriving as soon as Thursday. 
 
 Amano, who is from Japan originally, will meet with senior officials and stay one night, he told reporters this afternoon. He said he hopes to come back with "firsthand information" on the situation and address the issue of improving the flow of information to the IAEA. 
 
 Earlier today Amano urged the Japanese government to provide better information to the agency about the nuclear crisis. 
 
 4.58pm (1.58am JST): Australia has advised its citizens to consider leaving Tokyo and earthquake-affected areas, but has said its advice is not due to the threat of nuclear contamination. 
 
 The country's Department of Foreign Affairs and Trade said its advice to Australians had nothing to do with the threat from the damaged plant. 
 
 "We are providing this advice because of the continuing disruption to major infrastructure, its impact on the welfare of people on the ground and continuing aftershocks," its notice said. 
 
 5.36pm: Reuters reports that the US government is now advising its citizens who live within 80km of the Fukushima nuclear plant evacuate or take shelter indoors. The Japanese government has not altered its 20km exclusion zone. 
 
 6pm: It's 3am JST in Japan, here's a summary of events today so far: 
 
 • Tens of thousands of people are still missing since Friday's earthquake and tsunami. Around 850,000 households in the north of the country are still without power in near-freezing weather conditions, and water supplies are disrupted in the worst hit areas. The official death toll has reached 4,000 but the total number of dead is expected to exceed 10,000. 
 
 • A massive international rescue effort to help Japan find and aid survivors is gathering pace. Japan's foreign ministry said today that 113 countries and regions as well as 24 international organisations had offered help, as well as offering assistance to tackle the deepening crisis at the Fukushima nuclear site. 
 
 • Yukiya Amano, the head of the International Atomic Energy Agency, said the situation at the Fukushima Daiichi nuclear power plant is "very serious" and confirmed core damage at reactors 1, 2 and 3. Amano is to visit Japan as early as Thursday. 
 
 • Earlier on Wednesday, a fire broke out at reactor No 4, a day after a blast blew a hole in the building housing the reactor's spent fuel rods. White smoke seen from No 3 reactor – thought to be most at risk – is most likely to be steam from water being poured in to cool exposed fuel rods. 
 
 • Japanese authorities are resorting to desperate measures to cool down the damaged reactors. Plans for military helicopters to pour water onto a damaged reactor are being reconsidered, after an earlier attempt was aborted due to safety concerns. Police will attempt to add coolant to the No 4 reactor's spent fuel pool using a water cannon. 
 
 • Japan's government says radiation levels around the Daiichi site are not at levels to cause an immediate health risk, while the Japanese Red Cross says Tokyo is safe for international travellers. The World Health Organisation says there is no evidence of a significant spread of radiation from the crippled Fukushima plant. 
 
 • In a rare bright spot, the Nikkei share index gained 4.5% during trading on Wednesday as several major companies announced plans to reopen businesses. The country's central bank, the Bank of Japan, continued to inject trillions of yen to keep the economy functioning. 
 
 This is Richard Adams in the Guardian's Washington bureau taking over live blogging duties. 
 
 6.20pm: Tepco, the operator of the Fukushima Daiichi plant, is holding a press briefing and saying that a new power line that could solve the cooling problem at the plant is almost ready. 
 
 No details yet but presumably that could mean the company could reconnect the reactors to the grip and so operate their usual cooling functions. Let's wait and see. 
 
 6.33pm: The UK's Foreign Office is now advising that British nationals currently in Tokyo and to the north of Tokyo should consider leaving the area: 
 
 We advise against all non essential travel to Tokyo and north eastern Japan given the damage caused by the 11 March earthquake and resulting aftershocks and tsunami. Regarding the situation at the Fukushima nuclear facility, the most recent advice from the UK's Chief Scientific Adviser remains that for those outside the exclusion zone set up by the Japanese authorities there is no real human health issue that people should be concerned about. This advice is kept under constant review. However, due to the evolving situation at the Fukushima nuclear facility and potential disruptions to the supply of goods, transport, communications, power and other infrastructure, British nationals currently in Tokyo and to the north of Tokyo should consider leaving the area. 
 
 More FCO information here. 
 
 6.48pm: Some more details on the new power lines being laid to the Fukushima plant, from the Associated Press: 
 
 The operator of Japan's tsunami-crippled nuclear plant says it has almost completed a new power line that could restore electricity to the complex and solve the crisis that has threatened a meltdown. Tokyo Electric Power Co spokesman Naoki Tsunoda said early Thursday the power line to Fukushima Dai-ichi is almost complete. Officials plan to try it "as soon as possible" but he could not say when. The new line would revive electric-powered pumps, allowing the company to maintain a steady water supply to troubled reactors and spent fuel storage ponds, keeping them cool. The nuclear crisis has triggered international alarm and partly overshadowed the human tragedy caused by Friday's earthquake and tsunami that pulverized Japan's northeastern coastline. 
 
 7pm: The latest estimates from Japan's National Police Agency puts the tally of dead and missing at 12,000, with the death toll to date above 4,000. 
 
 According to a statement by the agency: 
 
 As of 10pm [JST], the death toll from the disaster stood at 4,277. The number of deaths stood at 2,207 in Miyagi Prefecture, the highest figure among the 12 prefectures where deaths have been reported. In Iwate Prefecture, 1,482 were killed. In Fukushima Prefecture, the death toll reached 533. Only 40% of the victims have been identified as of Wednesday morning, according to the NPA. At least 8,194 people are missing in six prefectures. The number stood at 3,318 in Iwate, 2,507 in Fukushima and 2,362 in Miyagi. 
 
 7.15pm: Tepco's delay in reconnecting the Fukushima plant to Japan's national grid is the subject of criticism from outside experts, writes my colleague Suzanne Goldenberg: 
 
 Kenneth Bergeron, who has done research on nuclear accident simulation at Sandia national labs in New Mexico, said the experience of Three Mile Island accident had demonstrated the importance of bringing in outside experts. "I am concerned that the management of this accident was left to very local hands for a very long time," he said. "Experience has shown in particular at Three Mile Island that sometimes the managers and operators in place when the accident has taken place are not well qualified. They may have the inability to see the big picture." In particular, he faulted the rescue effort for not immediately working to restore the power to the reactors' cooling systems. "What was really needed at Fukushima was restoration of the AC power to the emergency cooling system, and instead we saw them running fire hoses from the ocean. Time will tell whether that was the only option or not but a jerry-rigged arrangement like that sounds to me like a move or real desperation." 
 
 7.30pm: AP is reporting a very worrying comment by Greg Jaczko, chairman of the US Nuclear Regulatory Commission: 
 
 US nuclear agency chief says no more water in spent fuel pool at troubled Japan plant. 
 
 That presumably refers to No 4 reactor. Jaczko is currently giving a briefing on the nuclear plant crisis in Japan to the US Senate's committee on the environment and public works. (There's a live webcast of the briefing here.) 
 
 If Jaczko's statement is correct, then there is nothing to stop the exposed fuel rods from getting hotter and melting down. And Jaczko should know: the NRC has experts on the ground in Japan. 
 
 7.49pm: Jaczko's worrying comments below (see 7.30pm) are at odds with reports from the Japanese media saying that coolant continues to be added into the Fukushima reactors. 
 
 According to the last report from the Jiji Press agency, posted nearly three hours ago, states: 
 
 [Tepco] kept working to pump seawater into the pressure vessels of the No 1, 2 and 3 reactors of the Fukushima No 1 nuclear plant. But the water levels have not reached the top of the nuclear fuel rods, and portions of the fuel rods thus remained exposed. 
 
 On the other hand, the discrepancy between the US and official Japanese position might explain why the US has told its citizens to maintain a 50 mile (80km) exclusion zone around Fukushima, compared with the 20 mile (30km) zone imposed by the Japanese government 
 
 8pm: According to the Kyodo news agency, Japan's nuclear agency has said that the water level has been dropping in the No 5 reactor as well: 
 
 The agency said it will closely monitor data on the reactor to prevent the problems that occurred at other reactors. 
 
 Given what has happened elsewhere this isn't a surprise and we should expect the same thing in No 6 as well. Reactors 4, 5 and 6 were actually out of commission at the time of the earthquake and tsunami, but the danger remains because of the highly radioactive used fuel stored in the reactors. In the case of No 4, it may have had more spent fuel, and it was harmed by the nearby explosions in the 1, 2 and 3 reactors, which was most likely to cause of the first fire in No 4. 
 
 8.21pm: More on the comments on the Fukushima nuclear plant by Greg Jaczko, chairman of the US Nuclear Regulatory Commission, to a congressional committee in Washington: 
 
 We believe at this point that Unit 4 may have lost a significant inventory, if not lost all, of its water.... There is no water in the spent fuel pool and we believe that radiation levels are extremely high, which could possibly impact the ability to take corrective measures. 
 
 Jaczko also said there was the possibility of a leak in the spent fuel pool in reactor No 3, "which could lead to a loss of water in that pool", as well as a falling water level in the spent fuel level at the No 2 reactor. 
 
 According to Reuters, Jaczko said radiation levels around the site could give emergency workers "lethal doses" of radiation, forcing them to stay away: 
 
 "We believe that around the reactor site there are high levels of radiation," Jaczko said. "It would be very difficult for emergency workers to get near the reactors. The doses they could experience would potentially be lethal doses in a very short period of time." 
 
 8.40pm: Fukushima cannot possibly become a second Chernobyl disaster, explains Sir John Beddington, the UK's chief scientific officer, speaking to the British embassy in Tokyo: 
 
 [Even] if you then couple that with the worst possible weather situation ie prevailing weather taking radioactive material in the direction of greater Tokyo and you had maybe rainfall which would bring the radioactive material down - do we have a problem? The answer is unequivocally no. Absolutely no issue. The problems are within 30 km of the reactor. And to give you a flavour for that, when Chernobyl had a massive fire at the graphite core, material was going up not just 500m but to 30,000ft. It was lasting not for the odd hour or so but lasted months, and that was putting nuclear radioactive material up into the upper atmosphere for a very long period of time. But even in the case of Chernobyl, the exclusion zone that they had was about 30km. And in that exclusion zone, outside that, there is no evidence whatsoever to indicate people had problems from the radiation. The problems with Chernobyl were people were continuing to drink the water, continuing to eat vegetables and so on and that was where the problems came from. That's not going to be the case here. So what I would really re-emphasise is that this is very problematic for the area and the immediate vicinity and one has to have concerns for the people working there. Beyond that 20km or 30km kilometres, it's really not an issue for health." 
 
 9pm: Facebook user Jun Shiomitsu has been collating and translating into English Japanese Twitter messages sent out about people's experiences following last week's earthquake. You can read them on his Facebook page but here are a few translations: 
 
 I went out last night to help some friends who were volunteering as security personnel between Machida City and Sagami Ohno City. I saw total strangers, both young and old, helping each other along everywhere I turned and was heartened with an overwhelming feeling of encouragement. I was so touched I hid behind the toilets and cried. While most of the convenience stores near the station were closed because of the quake, there was just one Seven Eleven that was open. The employees had lit lots of candles and put them on the stores shelves. The cash register was not working and they could not take inventory, so the employees worked in threes, one reading up the item description and price, another punching the numbers into a calculator, and the last one using a flashlight to help them work. The store managed to operate both "cash registers" efficiently this way. Impressed! A goth youth with white hair and body piercings walked into my store and shoved several tens of thousands of yen [several hundred dollars ] into the disaster relief fund donation box. As he walked out, I and people around me heard him saying to his buddies, "I mean, we can buy those games anytime!" At that, we all opened our wallets and put our money into the donation box. Really, you cannot judge people by their appearances. 
 
 9.14pm: Japanese authorities have denied the claim by Greg Jaczko, chairman of the US Nuclear Regulatory Commission, that the No 4 reactor at Fukushima may have lost all its coolant. 
 
 AP reports Hajime Motojuku, spokesman for plant operator Tepco, as saying the "condition is stable" at the No 4 reactor. 
 
 9.29pm: A useful post from the journal Nature explaining the types of radiation and their effects, to help readers know their millisieverts from their microsieverts: 
 
 One of the most important and misunderstood aspects of radiation is that the effects are cumulative. That means that when thinking about health effects, the time of exposure is just as important as the dose. For example, the average person receives about 1-2 mSv per year without any bad effects, but if they received a does of 1-2 mSv/minute they would become sick in less than a day. The peak doses recorded at Fukushima Daiichi have been around 400 mSv per hour, enough to induce radiation sickness in about two hours' time. (Radiation levels at the site have since fallen, but continue to fluctuate). 
 
 9.51pm: The Guardian's Jon Watts is in Kitakami, Iwate Prefecture, finds that many of those hit by the disaster still lack blankets, food or fuel, raising fears of a full-blown humanitarian crisis: 
 
 Masaki Ohata, a pharmacist whose home in Kesennuma was destroyed by the tsunami, said the radiation threat was a lesser concern. "The nuclear meltdown is frightening. It's something you can't see that can hurt you. But frankly it is not as terrifying as the disaster I saw with my own eyes." Ohata has been sleeping in a room outside the city hall on a concrete floor with no blankets. The Guardian has spoken to dozens of refugees, all of whom were waiting for help that was yet to come on anything like an adequate scale. Some needed medicine. Others were desperate for sanitary wear. Many were cold because they lacked blankets and stoves. All were uncomfortable and unhappy about the lack of running water which meant they were having to relieve themselves in plastic bags. 
 
 10.10pm: Nuclear plant operator Tepco says it plans to try again on Thursday with its plan to drop water into the No 3 reactor by military helicopter. The frist attempt today was called off because of high radiation around the Fukushima Daiichi site, although the IAEA also had concerns about the method. 
 
 The damaged No 3 reactor remains the highest priority, because of the presence of Mox (Mixed oxide) fuel which contains highly dangerous plutonium. 
 
 10.24pm: Japan's giant car manufacturers remain closed in the wake of the traumatic earthquake and tsunami – but there was a sliver of good news from Toyota. 
 
 The company said it will keep its car production lines closed for another week, but said it will reopen its replacement parts factories on Thursday and the factories making parts for overseas production on Monday. 
 
 Nissan also said it is restarting car assembly on Thursday for as long as supplies lasts. 
 
 10.39pm: Greg Jaczko of the US Nuclear Regulatory Commission was buttonholed by journalists in Congress and pressed on his claims of no water remaining in a No 4 reactor's spent fuel pool, subsequently denied by Japanese officials. Jaczko says: 
 
 The information I have is coming from staff people in Tokyo who are interfacing with their Japanese counterparts. They believe the information they have is reliable. 
 
 The NRC has 11 staff currently working in Japan. Jaczko did also say: "It is my great hope that the information is not accurate." 
 
 10.54pm: NHK has more details on Tepco's attempts to lay new power lines to the Fukushima Daiichi nuclear plant and restart cooling systems: 
 
 The operator of the quake-damaged Fukushima Daiichi nuclear power plant says it is trying to install new power lines to reactivate its cooling systems in a desperate effort to stop the ongoing radioactive leakage. Tokyo Electric Power Company says it wants to start the work to install the new lines as early as Thursday morning. ... The top priority at the moment is restoring the functions of the cooling systems now that radiation is continuing to leak from the plant. Tokyo Power Electric Company says it is considering laying new power lines into the plant directly from cables of another power company. The company says it hopes to reactivate the cooling systems by connecting the cables to a makeshift switchboard and using them as an emergency power source for the systems. But the company says it was unable to carry out the work on Wednesday because of high readings of radiation in the compound. The company says it will try to complete the installation as soon as possible after reviewing the procedures in order to keep the workers' radiation exposure to a minimum. 
 
 11.08pm: Asahi Shimbun's English language site on Facebook has a description of the grim conditions facing refugees in the icy north of Japan, at the centre of the earthquake's devastation: 
 
 In Morioka, the mercury hit a low of minus 1.4 degrees. Throughout wide areas of the Tohoku region heavy snow forced evacuees inside evacuation centers. Many had fled their homes with little more than the clothes on their backs after the March 11 M9.0 earthquake and tsunami. Evacuees in many shelters were crammed into cold, uncomfortably tight quarters, raising fears of flu outbreaks. At municipal Daiichi Junior High School in Rikuzentakata, Iwate Prefecture, about 20 residents huddled around a large drum where a bonfire was burning. Here, at least, fuel was not a problem. "We have all the lumber we need," said one evacuee who had been at the shelter since the the first day of the disaster. He said that the fires were kept burning around the clock. With the school surrounded by homes flattened by the quake, wood was plentiful. 
 
 11.22pm: The New York Times gives its take on the differing Japanese and American views on the facts inside the Fukushima reactors: 
 
 The chairman of the United States Nuclear Regulatory Commission gave a significantly bleaker appraisal of the threat posed by Japan's nuclear crisis than the Japanese government, saying on Wednesday that the damage at one crippled reactor was much more serious than Japanese officials had acknowledged and advising Americans to evacuate a wider area around the plant than the perimeter established by Japan. 
 
 11.45pm: The Japanese yen has strengthened remarkably against the US dollar and other currencies such as the Australian dollar in overnight foreign exchange trading. 
 
 The yen now stands at its highest level against the US dollar since 1945, with just over 76 yen to the dollar, on a wave of buying in anticipation of Japanese companies selling dollar-denominated assets and moving funds back into yen. 
 
 The strengthening yen helped push Japanese share prices down, with the stronger yen making Japan's exports more expensive. The government may intervene in the foreign exchange market and sell yen to push its value down. 
 
 Meanwhile, the Bank of Japan injected trillions of yen in the country's financial system for the fourth day in a row. 
 
 12.17am: Kyodo news agency is reporting that Japanese Self-Defense Forces helicopters are in the air monitoring radiation levels above the Fukushima Daiichi reactor. 
 
 12.28am: The International Atomic Energy Agency has more bad news that temperatures within Fukushima Daiichi reactors number 4, 5 and 6 have been rising. 
 
 Until today there had been little to say about the 5 and 6 reactors, which along with reactor No 4 had been shut down at the time of the earthquake. But all three contain spent fuel. 
 
 12.42am: The search for bodies continues along Japan's northeast coast as survivors and rescue teams hunt for the missing. This AP story is filed from Miyagi prefecture: 
 
 Line after line, a list on the wall of city hall reveals the dead. Some are named. Others are identified only by a short description. Female. About 50. Peanuts in left chest pocket. Large mole. Seiko watch. Male. 70-80 years old. Wearing an apron that says "Rentacom." One set catches the eye of Hideki Kano, a man who appears to be in his 30s. "I think that's my mom!" he says. He rushes out into the snow, headed for a makeshift morgue. The list in Natori, and others along Japan's northeast coast, will only get longer. Five days after the 9-magnitude earthquake and tsunami, the official death toll is more than 4,300. More than 8,000 people are still missing, and hundreds of national and international rescue teams are looking for them. In the industrial town of Kamaishi, 70 British firefighters in bright orange uniforms clamber over piles of upturned cars to search a narrow row of pulverized homes. They wear personal radiation detectors amid fears of leaks from damaged nuclear plants far to the south. One woman's body is found wedged beneath a refrigerator in a two-story home pushed onto its side. "Today and tomorrow there is still hope that we will find survivors," says Pete Stevenson, head of the British rescue crews. "We'll just keep on carrying out the searches." 
 
 1am: Broadcaster NHK is reporting that water tankers are near the Fukushima power plant, preparing to spray water into the No 4 reactor: 
 
 High-pressure water spray vehicles will aim at the fuel storage pool through a hole in the wall of the No 4 reactor housing structure. The police unit will wear protection gear provided by the Self-Defense Forces and maintain safety measures, such as checking radiation levels during the operation. 
 
 1.14am: The Guardian's Suzanne Goldenberg looks at criticism of how Japan authorities have tackled the nuclear crisis emerging at Fukushima – and talks to the man who had to clean up Chernobyl, who has a chilling logic: 
 
 Yuli Andreyev, former head of the agency tasked with cleaning up after Chernobyl, told the Guardian that the Japanese had failed to grasp the scale of the disaster. He also said the authorities had to be willing to sacrifice nuclear response workers for the good of the greater public, and should not only be deploying a skeleton staff. "They don't know what to do," he said. "The personnel have been removed and those that remain are stretched." 
 
 Further down: 
 
 The decision to evacuate personnel when radiation levels spiked also attracted criticism. Arjun Makhijani, president of the Institute for Energy and Environmental Research, said: "How long can 50 workers last in trying to manage a disaster in four reactors?" 
 
 1.26am: Reuters has a round-up of the aftermath of Japan's earthquake disaster in numbers: 
 
 Death toll 
 
 The death toll is expected to exceed 10,000, with northeastern prefectures of Miyagi, Iwate and Fukushima most severely hit. At least 4,314 people were confirmed dead, but more than 8,600 people are still missing, Japan's Asahi newspaper quoted police as saying on early Thursday. 
 
 People evacuated 
 
 More than 440,000 people have been evacuated, NHK says. Hundreds of people are waiting for help in isolated areas and have no access to food. 
 
 People without power or water 
 
 About 850,000 households in the north are still without electricity in near-freezing weather, Tohuku Electric Power Company says. The government says at least 1.5m households lack running water. 
 
 Buildings damaged 
 
 More than 100,000 buildings have been damaged, including at least 7,400 completely destroyed, public broadcaster NHK says. 
 
 Economic impact 
 
 Citigroup expects 5tn-10tn yen in damage to housing and infrastructure, while Barclays Capital estimates economic losses of 15tn yen ($183bn) or 3% of Japan's GDP. 
 
 International aid 
 
 According to Japanese foreign ministry, 114 countries and 24 international organisations have offered assistance. 
 
 1.34am: Helicopters are now dumping water on the Fukushima Daiichi No 3 reactor in a desperate attempt to add coolant, Kyodo reports: 
 
 A Self-Defense Forces helicopter dropped water on the troubled No 3 reactor of the Fukushima nuclear power plant on Wednesday as it is feared the reactor may have released radioactive steam due to damage to its containment vessel. 
 
 According to AP, it's more than one helicopter. 
 
 1.45am: A UN forecast of the movement of a radioactive plume coming from the Fukushima reactors shows it possibly reaching California on Friday, the New York Times is reporting: 
 
 On Wednesday, the agency declined to release its Japanese forecast, which The New York Times obtained from other sources. The forecast was distributed widely to the agency's member states. But in interviews, the technical specialists of the agency did address how and why the forecast had been drawn up. "It's simply an indication," said Lassina Zerbo, head of the agency's International Data Center. "We have global coverage. So when something happens, it's important for us to know which station can pick up the event." 
 
 The report makes clear that any likely plume would have "extremely minor health consequences in the United States". 
 
 1.51am: News of a radioactive plume that could reach California may only serve to increase sales of iodide pills in the US. But Twitter warns: 
 
 Potassium Iodide Pills (KI) are NOT antiradiation pills! Americans should NOT be taking KI as it can have negative side effects for some! Nuclear Fissionary 
 
 Fissionary 
 
 
 
 That tweet comes from a pro-nuclear blog Nuclear Fissionary. 
 
 2.04am: How difficult has the tsunami damage made rescue efforts? Australian emergency crews in Japan are digging through ice to rescue bodies trapped in Minamisanriku, where more more than half of the coastal town's 17,000 residents are still missing. 
 
 ABC News reports that until yesterday the crews were having to walk 20km there and back each day to the rescue site, until the Japanese military were able to help. 
 
 2.14am: So far there have been four attempts by helicopters to dump giants buckets of water on the No 3 reactor at Fukushima Daiichi, and only one has succeeded in hitting the target. 
 
 From Asahi: 
 
 A Ground Self-Defense Force helicopter dropped water on the No 3 reactor at the Fukushima No 1 nuclear power plant at 9.48am [JST]. Two helicopters flew over the reactor four times to drop water. The helicopters scooped up seawater in an attached bucket with a capacity of 7.5 tons. The four water drops ended the helicopter operation. Workers on the ground were planning to begin spraying water from a police water cannon. A GSDF helicopter tried to drop water over the crippled reactor Wednesday, but had to abandon the plan because of the high radiation levels over the reactor. 
 
 2.19am: Power supply to the Fukushima plant may partially resume later in the afternoon, thanks to a new power line being laid by Tepco, Kyodo news agency is reporting. 
 
 2.26am: The disturbing news of some of those who died in the panic and chaos following the earthquak and tsunami last Friday. 
 
 Fukushima Prefecture is looking into the deaths of 14 hospital patients at an emergency shelter where they had evacuated. According to broadcaster NHK, officials say 128 hospital patients were taken on Monday to a relief shelter in a high school in Iwaki city. Two of them reportedly died en route, and 12 others died shortly after arriving at the shelter. 
 
 2.35am: Keiji Takeuchi, a senior staff writer at Asahi Shimbun newspaper, has a column which raises the question of the likely cost in human lives from the deadly effort required to tame Fukushima's reactors: 
 
 During the Chernobyl accident in 1986, sand was poured from the air by helicopter over the exposed reactor core. On the ground, many people worked at close range to the crippled reactor. However, the massive discharge of radioactive materials was stopped in one week. Without that death-defying effort, the world would have been contaminated to a greater degree. In the wake of that accident, the topic of working under very high radiation levels was also discussed in Japan. However, that debate faded because it would have involved the fundamental social issue of whether a democratic state can order people to do work harmful to their health. There was also the myth that major accidents just do not happen in Japan. Now, however, we face an emergency situation. A quick decision and response is required. 
 
 2.46am: Japanese prime minister Naoto Kan and US president Barack Obama held a 30 minute phone conversation this evening, with Obama promising to send more US nuclear experts to Japan, and offered further aid to help with the country's massive relief effort. 
 
 3.04am: Mizhuo Bank says all its automated teller machines have stopped working across Japan. 
 
 3.18am: 
 
 Public distrust in the government is "growing day by day" over its handling of the crisis, writes Takuya Karube of Kyodo News agency. 
 
 The commentary offers more details of the in-fighting between the government and Tepco which led to Japan's prime minister Naoto Kan and chief cabinet secretary Yukio Edano summoning executives of the power company and urging them to share information. (You'll recall that Kan was heard shouting "What the hell is going on?" at the company.) 
 
 Kiyoshi Sasamori, a former head of the Japanese Trade Union Confederation, quoted Kan as saying during their talks Wednesday, ''I went into the head office because the utility company lacks a sense of crisis as the plant's operator.'' 
 
 This is Tania Branigan in Beijing taking over from Richard Adams. 
 
 If you're just joining us, it's 3.45am in London, 12.45pm in Japan, and this is a quick summary of events: 
 
 • The official death toll following Friday's earthquake and tsunami has reached 5,000 but the total number of dead is expected to exceed 10,000. Around 850,000 households in the north of the country are still without power in near-freezing weather conditions, and water supplies are disrupted in the worst hit areas. 
 
 • A massive international rescue effort to help Japan find and aid survivors is gathering pace, but supplies remain short in many places. President Obama has just offered to send more nuclear experts and assist long term recovery efforts in a 30 minute phone conversation with Japanese prime minister Naoto Kan. 
 
 •Japanese self-defence force helicopters have been dropping water on unit 3 at the damaged nuclear plant. They appear to have been struggling to hit their target. The airdrop has finished and police water cannons will now be used. 
 
 • The move follows reports that Greg Jaczko, chairman of the US Nuclear Regulatory Commission, said there was "no water" in the spent fuel pool at troubled Japan plant. There is a lot of concern about the state of the pool at unit 4 and Kyodo news agency says the water level has dropped in unit 5 too, citing Japan's nuclear agency. 
 
 • Tepco officials are running a new powerline to the plant and say power could resume as early as this afternoon. Experts have said powering the cooling system is essential to get the plant back under control and have criticised the company's failure to deal with the issue earlier. 
 
 • The UK – which last night urged citizens in or north of Tokyo to consider leaving – is now echoing US advice to remain outside an 80km radius of the facility "as an additional precautionary measure". The embassy in Tokyo adds: "The most recent advice from the UK's Chief Scientific Adviser remains that for those outside the exclusion zone set up by the Japanese authorities there is currently no real human health issue that people should be concerned about." 
 
 • Chief government spokesman Yukio Edano says it still believes its measures are appropriate (they are: a 20km evacuation zone and a 20-30km zone in which people should remain indoors). 
 
 3.57am (12.57pm JST): On NHK, Professor Akira Yamaguchi of Osaka University has offered a somewhat gloomy analysis of the attempts to douse the fuel pool with water using helicopters. The images suggested it was "highly likely" the effort was insufficient, he said, because the spent fuel pool is believed to have been almost empty and when water is dropped from above a lot of it gets lost en route. He added: 
 
 
 
 "7.5 tonnes of water has been dumped [it seems]. We do not know the size of the pool, but judging from other examples it probably holds 2000 tonnes. It does not mean the pool needs to be completely full, but maybe a third of the tank's capacity is needed. 
 
 It [the water dumping] needs to be done continuously." 
 
 4.08am (1.08pm JST): Reuters is reporting that the US government has authorised the voluntary departure of the family members of embassy staff. The State Department is also chartering aircraft to Tokyo to help Americans leave Japan, it says. 
 
 Given the growing concern, it is worth a reminder that we have a piece looking at what the radiation levels actually mean. 
 
 And, as we have said, the bigger issue for many survivors right now is the inadequate supply of food, fuel and medicine. 
 
 4.31am (1.31pm JST): Further bad news for survivors in the quakezone: more snow is expected in Miyagi and Iwate prefectures today, though forecasters say the cold front should move away by Friday evening. 
 
 If you missed his terrific report earlier, the Guardian's Jonathan Watts has reported from Iwate on the impact of mid-winter temperatures and a shortage of supplies: 
 
 "What we urgently need now is fuel, heavy and light oil, water and food. More than anything else, we need fuel because we can't do anything without it. We can't stay warm or work the water pumps," said Masao Hara, the mayor of Koriyama city, in Fukushima prefecture... As far as the refugees are concerned, the balance of priorities is wrong. Masaki Ohata, a pharmacist whose home in Kesennuma was destroyed by the tsunami, said the radiation threat was a lesser concern. "The nuclear meltdown is frightening. It's something you can't see that can hurt you. But frankly it is not as terrifying as the disaster I saw with my own eyes." 
 
 4.42am (1.42pm JST): The office of the Japanese prime minister is using its English language Twitter account (@JPN_PMO) to reassure people in light of the US warning to stay more than 80km away from the Fukushima plant or take cover: 
 
 We believe they made a more conservative assessment of the radiation level from perspective of protecting US citizens. Mr. Edano: Japan Gov't has asked residents living btw 20 & 30 km from the plant to take shelter as a precaution. No impact on human body at present even if u staying outside for 24 hrs. 
 
 4.48am (1.48pm JST): Reuters reports that finance leaders and central bank governors from the G7 nations will hold a teleconference on Friday at 7am JST tomorrow (10pm GMT tonight for those in the UK). 
 
 "Japan will explain the damage from the earthquake, financial market movements and government efforts," Finance Minister Yoshihiko Noda told reporters. 
 
 5.01am (2.01pm JST): The BBC is carrying a disturbing report from Minamasoma, just 20km away from Fukushima No 1 plant, where residents say they are running short of supplies and complain that no one is helping them. Relief teams are reluctant to go in - remember that people 20km to 30km away from the plant have been told to stay inside - and inhabitants say there is too little fuel for everyone to leave. The footage appears to have been shot by a Japanese crew. 
 
 The town's mayor, Katsunobu Sakurai, is scathing: 
 
 
 
 "We were not told when the first reactor exploded. We just heard about it on TV. The government doesn't tell us anything. We are isolated. They are leaving us here to die." 
 
 5.27am (2.27pm JST): A quick response to some of the queries people have raised in the comments section: @kansaimon, we did indeed report on Naoto Kan shouting at Tepco executives earlier this week; I have revised that entry accordingly. 
 
 @erudition comments on the danger posed by spent fuel rods - as you say this is a big issue; we have reported on it in several places - notably in this piece by Suzanne Goldenberg. There is also a very clear explanation of the issues from the All Things Nuclear blog run by the Union of Concerned Scientists. 
 
 @gluino says Britons were advised to consider leaving Tokyo (and areas north of the capital) for reasons other than possible radiation. In fact, the Foreign Office advice specifically mentioned the "evolving situation" in Fukushima as well as potential disruptions to transport, supplies, communication and power. 
 
 As we mentioned earlier, it updated its advice this morning, urging Britons to remain outside an 80km radius of the plant "as an additional precautionary measure" or take shelter if they stayed within 30-80km. It said people within 80km of Fukushima should contact its Japan emergency hotline on +44 20 7008 0000 for further advice. 
 
 5.35am (2.35pm JST): The New York Times has a useful graphic explaining how many people are affected by the Japanese exclusion and take-shelter zones and the US evacuation recommendation. It says the US recommendation to its nationals (an 80km radius) would affect 1.9 million people if Japanese residents followed suit. 
 
 5.53am (2.53pm Japan): The Guardian's Justin McCurry in Japan has filed an update on the situation at Fukushima. His full story will be up shortly. 
 
 
 
 Attempts to cool down a stricken reactor at the Fukushima Daiichi nuclear plant suffered an early setback on Thursday after seawater dumped from the air failed to bring down radiation levels. Radiation readings taken 20 minutes after self-defence force helicopters doused the plant's No. 3 reactor remained unchanged, Tokyo Electric Power [Tepco] said, according to Kyodo news agcncy. 
 
 6.00am (3pm JST): NHK has another worrying report of shortages, this time from Minamisanriku, one of the towns worst hit by the tsunami. The mayor told the broadcaster it needs more fuel "for the very survival of its people...It is going to be a long battle." 
 
 6.19am (3.19pm JST): Kyodo points out that the yen briefly spiked to a new record high of 76.25 against the US dollar in Sydney today , having previously risen to 79 yen in New York (the previous postwar high was 79.75 yen). Although this might sound counter-intuitive, the assumption is that Japanese companies will want to repatriate funds overseas to pay for the impact of the earthquake, tsunami and nuclear crisis. 
 
 6.40am (3.40pm JST): Justin McCurry's story on this morning's water drop on to the overheating fuel pool at unit 3 is here . 
 
 Attempts to cool down a stricken reactor at the Fukushima Daiichi nuclear plant suffered an early setback on Thursday after seawater dumped from the air failed to bring down radiation levels. Radiation readings taken 20 minutes after self-defence force helicopters doused the plant's No 3 reactor remained unchanged, Tokyo Electric Power [Tepco] said, according to Kyodo news agcncy. The use of Japanese military helicopters to drop seawater onto the plant's reactor marked the opening of a new front in the battle to avert nuclear meltdown. 
 
 7.07am (4.07pm): Some good news on the recovery efforts: NHK reports that telecoms firms are sending mobile receivers, power services and phone chargers into the disaster zone. That should help with logistics, but could also be an important boost to morale, allowing more survivors to make contact with friends and loved ones. 
 
 7.20am (4.20pm JST): Kyodo says Japanese officials are "baffled" by the warning from the chair of the US nuclear regulatory commission that there was no water in the spent fuel pool in reactor 4, which we reported earlier. The NRC has dispatched experts to assist Japan as it battles the crisis at the nuclear plant. 
 
 ''There was a slight delay conveying to the U.S. side the information about whether or not there is water'' in a pool holding spent nuclear fuel rods at the quake-hit Fukushima No. 1 nuclear plant, Chief Cabinet Secretary Yukio Edano told a news conference... A Ground Self-Defense Force chopper, which doused the overheating spent nuclear fuel pool with water Thursday morning at the No. 3 reactor, found that water is left in the pond at the No. 4 unit, according to the plant operator Tokyo Electric Power Co... Based on the NRC's finding, the U.S. Embassy in Japan has asked American citizens living within an 80-kilometer radius of the Fukushima No. 1 power station to evacuate as a precautionary measure... Japan's Nuclear and Industrial Safety Agency said it believes the U.S. evacuation recommendation is ''not appropriate'' and will bolster information sharing with U.S. authorities so as not to cause misunderstandings. 
 
 7.46am (4.46pm JST): The Daily Yomiuri helps to explain why many emergency shelters are still low on food, fuel and other essentials. It says the supplies are reaching distribution depots, but officials are struggling to get them to the people who need them because of fuel shortages and because many routes are inaccessible due to quake and tsunami damage.
– When officials decided to vent radioactive steam from one of the damaged nuclear power plants in Japan, they knew it could result in a hydrogen explosion. And, even though an explosion is exactly what happened, the decision was still the best option for avoiding a total meltdown, the AP reports in an interesting piece that traces the chain of events from Friday, when the earthquake damaged the Fukushima Dai-ichi nuclear complex, to this morning, when a total of six reactors were placed under a state of emergency. More from Japan: The estimated death toll is more than 10,000 as of today, with the prime minister calling this disaster Japan’s worst crisis since World War II, the AP reports. The confirmed dead number more than 1,800. Nuclear plant operators dumped sea water into two reactors in a last-ditch attempt to keep temperatures down, as officials warned a second explosion could occur, but would not pose a health threat. Experts confirm to Reuters that “this is not a serious public health issue at the moment,” and that the winds will likely carry contamination to the Pacific, where it will not threaten any other nations. The next crisis facing Japan could be an economic one, Reuters reports. Automakers, electronics firms, and oil refineries have been forced to suspend operations at some of their factories, and many companies are not sure how soon they will be back up and running. Even so, experts say the economy could bounce back in months. Click for more on Japan.