Divers searching the wreck of the Costa Concordia have found the body of a woman in the stern of the partially submerged Italian cruise ship, the country's Coast Guard said, raising the confirmed number of deaths to 12.

Another 20 people remain missing, eight days after the vessel hit rocks off the coast of Italy, near the island of Giglio.

Italian Coast Guard Cmdr. Cosimo Nicastro said the woman was wearing a life vest and her body was found in a narrow underwater corridor near an evacuation staging point at the ship's rear.

Her nationality and identity were not immediately known. The body was taken by helicopter to the port of Santo Stefano on the island.

News of the discovery came after divers resumed the search for bodies on Saturday, with help from navy explosive experts using micro charges to blow through windows of the ship, which is lying on its side in 20 metres of water.

Divers are using cameras to search areas of the ship where access has been difficult.

"They're going into every single cabin. It takes 45 minutes to look into each of those cabins," freelance journalist Sabina Castelfranco, who attended Saturday's Italian coast guard briefing, told CBC News.

"In the submerged part they're doing targeted searches, basically using witness accounts regarding the passengers still missing as to which areas and which paths they may have followed."

The Italian government on Saturday announced it has appointed the chair of its civil defence department, Franco Gabriel, to co-ordinate the search for bodies and the fuel recovery.

At the same time, Italian officials have confirmed the presence of light fuel in the sea around the Costa Concordia that appears to have come from machinery on the cruise ship.

However, Nicastro said there is no indication that any of the nearly 2,200 tonnes of fuel oil has leaked from the ship's double-bottomed tanks.

Nicastro said the leaked substance appears to be diesel, which is used in rescue boats or as lubricants on machinery. There are 167 tonnes of diesel and lubricants on board.

He described its presence in the sea as "very light, very superficial" and appearing to be under control.

Crews were removing oil-absorbing booms used to prevent environmental damage in case of a leak. Originally white, the booms were greyish. Tug boat crews had laid new booms around the ship overnight.

Italy's environment minister has warned that if the tanks break, heavy fuel would escape and block sunlight vital for marine life in the seabed.

There are fears the vessel may slip from its rocky perch and plunge about 27 metres into deeper water, so rescuers have for the most part been working only above the ship's waterline.

On Tuesday, Italian naval divers set off explosives to create four small openings in the hull to speed the search.

The ship shifted again on Friday, forcing the temporary suspension of diving operations, but the search resumed Saturday morning after data indicated the ship had stabilized.

The $450-million liner was carrying more than 4,200 passengers and crew when it ran aground Jan. 13.

Dutch salvage experts will wait until the search for bodies is over before they can start to pump fuel from the wreck.

Officials have said it would likely take crews two to four weeks to remove all the fuel.

More than 100 passengers have joined a class-action lawsuit against Costa Cruises, which is owned by the U.S.-based Carnival Group. The BBC reports they're seeking up to $15 million. The suit is expected to be filed in a Miami court next week.