The death toll of the Italian cruise liner wreck rose to 12 on Saturday after the body of a woman was found in the ship that ran aground off the country's western coast a week ago, local media said.

The corpse, which was reportedly wearing a life jacket, was found on the fourth deck of the Costa Concordia after specialist divers accessed to the capsized vessel using controlled explosives.

Twenty people are still missing after the ship with over 4,229 people on board crashed into a rock last Friday in shallow waters near Giglio island off the Tuscany coast, ripping a hole in its hull.

On Saturday, divers also recuperated the captain's strongbox and personal belongings, as well as the video cameras of command quarters, which may reveal further details on the tragedy in ongoing investigations.

Captain Francesco Schettino, who was said to have left the ship before all passengers had evacuated refusing to coordinate rescue operations, has been put under house arrest with charges of manslaughter and abandoning ship.

During his interrogation Schettino reportedly claimed he had communicated promptly the serious accident to the company owner of the ship, Costa Cruises, which had not responded to the appeal adequately.

Fears are now growing that the 290-meter-long cruise liner could slip off a ledge into deeper water, with consequent further damage of its inside structures and fuel leaks from its tanks.

Civil Protection Chief Franco Gabrielli said swift action needs to be taken to avoid a huge environmental disaster, "as ambient contamination has already happened."

"Inside the ship there are still 2,400 tons of fuels, but also oils and solvents, detergents, and all the necessary things for a community of 4,000 people,"he told a press conference at Giglio island.

A specialist team from Dutch company SMIT is ready on the spot to start pumping the fuels from the vessel, which will take at least one month.