Indian investigators yesterday combed through the twisted and torn wreckage of rail carriages ripped apart by co-ordinated bombings that killed 200 people and wounded hundreds during Mumbai's evening rush hour.

The eight bombs tore through packed trains, stunning a city that embodies India's global ambitions, presenting itself to the world as a crowded and cosmopolitan metropolis where bankers dine with movie stars and fashion models party until dawn.

As Mumbai's 16 million people struggled to regain their footing, suspicion for the blasts fell on Kashmiri militants who have in the past carried out near-simultaneous attacks on Indian cities, including bombings last year at three markets in New Delhi that killed 59 people.

But two of the main Islamic militant groups in the Himalayan region - Lashkar-e-Tayyaba and Hezb-ul-Mujahedeen - said in separate statements that they had nothing to do with the Mumbai bombings or a series of grenade attacks in Kashmir that killed eight people.

The Times of India reported that Indian intelligence officials believe two groups, the Kashmiri militant group Lashkar-e-Tayyaba and the banned Students Islamic Movement of India, were responsible for the blasts. Both groups were blamed for a series of Mumbai bombings in 2003.

The attacks drew condemnation from around the world, and Indian Prime Minister Manmohan Singh said "terrorists" were behind the bombings, which he called "shocking and cowardly".

Indian stocks, meanwhile, rose 1.3 per cent in morning trading yesterday, recovering from an early drop.

With the annual monsoon leaving the Arabian Sea port overcast and damp, police picked through the mangled train cars, placing evidence in blue plastic bags and shooing away curious onlookers.

"We are just trying to establish what kind of explosives were used and where exactly the bombs were placed, but it appears they were kept in the luggage racks," said police inspector Yeshwant Patil, who was helping sift through one wrecked train carriage.

His assessment matches with initial reports that most of the victims suffered head and chest injuries, presumably from blasts above their heads.

But even as authorities said they were trying to determine the nature of the bombs, the CNN-IBN television news channel, citing police, reported that powerful RDX explosives were used, and that police found timers at one of the station's hit.

Governments around the world tightened security in cities from New Delhi to New York after the eight blasts, which struck seven trains within minutes of each other during the early evening rush hour. India's cities remained on high alert today.

Commuter transit systems have been tempting targets for terrorists in recent years, with bombers killing 191 in Madrid in 2004 and 52 in London last year. Mumbai suffered blasts in 1993 that included the Bombay Stock Exchange, killing more than 250 people.

Residents overcame their fears and returned to the trains. However, there was none of the usual crush on the trains, which serve some six million people a day, making it one of the world's most crowded rail networks.

In many first class carriages - the target of the bombings - there were fewer than half the usual 60 to 70 people.

"Our trust in Mumbai has been shattered, we had always thought trains were safe, but what can we do - in this city trains are the lifeline," said Brijesh Ojha, 35, who boarded the train at Bandra station, where the first blast occurred.

"They can't scare us this way," he said.

Worried residents searched through the night for missing friends and relatives. Dozens of people stood in hospitals, carrying pictures of the missing.

"We have gone to four hospitals, he would have called by now," sobbed Shakuntala Wari who was looking for her 24 year-old son, Vikas, at the Bhabha hospital near Bandra.

She had also visited a morgue. "I'm just very scared what happened to him."

Others crowded around hospital notice boards poring over lists of the dead.