The rear restaurant alone occupies three different floors, and rescuers say they constantly have to dodge moving debris.
"This isn't an easy mission on such a big and complex ship," said Giuseppe Minciotti, director of the Italian school for cave divers and head of a rescue unit from Vicenza.
"There are lots of things moving around down there -- furniture, beds, cupboards. It is very dangerous and we have to be very careful," Minciotti told Reuters television in an interview on a ferry taking him back to the island of Giglio.
Speleologists, as they are known, are used to diving in dark and enclosed spaces. The ship's hallways, cabins and dining rooms are similar to caves -- but caves do not have floating furniture or doors that may be jammed shut.After pulling out three survivors on Sunday, two-man teams of speleologists on Monday explored the wreck, half-submerged and resting on its starboard side.
The divers wear wetsuits reinforced with Kevlar -- the same material used to make bullet-proof vests -- and have a guide line to open water, just as they do when exploring caves.
Choppy seas caused the huge ship to slip on the rocky slope on Monday, forcing a two-hour suspension of rescue operations.
"The divers are inside and they're in very grave danger because if the ship were to shift while they were inside, it would be exceedingly dangerous," said Environment Minister Corrado Clini.
Most of the part of the ship that is still above water has already been searched, according to Luciano Roncalli, a firefighter in the squad coordinating the search and rescue efforts.
They divers hope to find survivors living in air pockets in the submerged areas. They will also carry out the grim task of locating corpses of those not rescued in time.Officials on Monday decided not to allow night diving because of the bad weather, and the ships' teetering along the slope of undersea rock.
The weather is forecast to worsen, with a high-sea warning for Thursday.
