(CNN) -- Mammoth cruise ships can be difficult to get around, even in the best of circumstances. In the worst -- which is how one might describe the situation aboard the listing Costa Concordia -- they are near impossible.





Yet even before the sun rose Monday, about 120 rescue personnel were out in or around the liner that hit rocks near Tuscany and rolled spectacularly on its side.





They were in a race against time, and in a battle with numerous challenges, to try to save survivors or at least recover the bodies of the passengers and crew members who are still missing.





Overheard on CNN.com: Worst-case scenario





The search was temporarily suspended by noon Monday, after authorities said the vessel had begun to sway, making it dangerous for the crews. But it resumed a short time later, despite a forecast calling for increasingly strong winds that Coast Guard spokesman Filippo Marino said had rescuers worried.





They are "working in very, very bad conditions," said Luciano Roncalli of Italy's national fire service. "It's cold, of course. It's dark during the day and the night. ... It's really, really dangerous."





Authorities have said that at least six people died after the Costa Concordia hit rocks Friday night off the tiny island of Giglio, where nighttime temperatures have recently dipped below freezing.





A total of 29 people -- four crew members and 25 passengers -- are still unaccounted for from the listing cruise ship, Italian coast guard chief Marco Brusco said Monday, according to Italy's ANSA news agency. That figure includes two of the 120 Americans who were aboard the ship, the U.S. Embassy in Italy said.





Now turned on its side, the ship is roughly half-submerged. Rescuers hope is that any survivor has found refuge above water, or perhaps in an air pocket, and can be brought out alive.





"There could still be people locked into compartments ... where they can't physically move because of the twisting of the metal," said Butch Hendrick, president of the diving safety company Lifeguard Systems.





In its current state, the Costa Concordia resembles a dark, convoluted cave -- with its countless nooks and crannies and few ways to easily escape. Six underwater cave rescue divers are working among the rescue personnel.





The divers are likely equipped with twice as much oxygen as regular scuba divers, have a guideline nearby in case they need help finding a way back to safety, and have knives and whatever lights they can carry or wear, said Robert Laird, a co-founder of the International Underwater Cave Rescue and Recovery group.





Still, whatever equipment and precautions they take, "what they are doing is extremely difficult," he said.





"If you do not have the right frame of mind to deal with being in the dark and in tight closed spaces, then you're (in trouble)," said Laird, who has dived in many caves and ships, though neither he nor his group are involved in the Italian operation.





Unlike open water divers, these divers don't have the luxury of coming up for air anytime they want, and they can't count on the help of sunlight.





Laird said he expects that, besides being pitch-black, the water in the ship teems with debris.





"They could swim right by a dead body and not even see it," Laird said.





Rescuers are navigating a seeming labyrinth.





The Concordia is practically a skyscraper in two directions: 17 decks high and 951 feet long.





Emergency personnel are aiming to look into 1,500 cabins and all around the ship's many other public spaces, including eight bars, five restaurants, four swimming pools, a casino and more. Hendrick, a veteran of many such rescue dives, estimated it could take a couple of weeks for the whole ship to be checked.





"It's enormous," said Richard Bordoni, another member of the Italian national fire corps. "They have to stay safe, and it takes them a long time to go down a corridor."





Late Sunday, the
what is practically a skyscrapper When was the search suspended? What length is the boat? what did the diving expert say What is the size of the concordia? What is the reason for the suspension? How long could the operation take? the rescue operation resumed despite what
The Concordia by noon Monday, 951 feet long. "There could still be people locked into compartments ... where they can't physically move because of the twisting of the metal," 17 decks high and 951 feet long. the crews. a couple of weeks a forecast calling for increasingly strong winds
question: what is practically a skyscrapper, answer: The Concordia | question: When was the search suspended?, answer: by noon Monday, | question: What length is the boat?, answer: 951 feet long. | question: what did the diving expert say, answer: "There could still be people locked into compartments ... where they can't physically move because of the twisting of the metal," | question: What is the size of the concordia?, answer: 17 decks high and 951 feet long. | question: What is the reason for the suspension?, answer: the crews. | question: How long could the operation take?, answer: a couple of weeks | question: the rescue operation resumed despite what, answer: a forecast calling for increasingly strong winds