Two South Korean honeymooners were rescued on Sunday from a cruise ship wreck on an Italian island as emergency crews searching for dozens missing said they could hear another voice inside.

Rescuers said the survivor was an Italian man on the third deck and he was being helped to safety inside the half-submerged Costa Concordia luxury liner, which crashed into rocks on Friday with more than 4,200 people on board.

Two French passengers and one Peruvian crew member have been confirmed killed, apparently after jumping into the chilly Mediterranean waters with dozens of others in a chaotic evacuation.

"We heard a voice from the exposed part," Luca Carli said, adding that the rescuers had begun hearing sounds at around 7:00 am (0600 GMT).

"We're trying to get there but it's a very, very complicated operation," Carli said, adding that the man was a public security officer.

He said the South Korean honeymooners had been evacuated by helicopter and were in 'perfect condition'.

"They were in their cabin, we still don't understand why," he added.

Daniele, one of around 20 army divers at the scene, in Giglio harbour said: "We've just started searching in the submerged part of the ship. It will take a long time."

"This is our job. We're experts in recovering bodies from submarines and shipwrecks. We've been briefed on the layout of the ship and all the cabin doors can be opened with a hydraulic mechanism," he said.

"It's very possible there are air pockets in the submerged part," he added.

Cosimo Nicastro, a spokesman for the coast guard, told reporters on Saturday: "This is a risky operation. The ship is in waters that are 30 metres (100 feet) deep but it could slowly slip into the sea and sink completely."

"We are talking about 50 or 60 people who are still missing" off the island of Giglio in Tuscany, he said. Interviewed by news channel SkyTG24 on Sunday, Nicastro declined to give a figure for those now believed to be missing.

Nicastro said some survivors may not have been counted properly but that others could have been trapped in their cabins or in other areas below deck.

Investigators arrested the ship's captain on Saturday and were to begin analysing the 'black box' recovered by rescuers, which logged all of the 291-metre long ship's movements as well as conversations between personnel.

The captain, Francesco Schettino, told Italian news channel TGCOM that the ship hit a rock that was not on the charts and that he had tried to save as many people as possible.

First officer Ciro Ambrosio was also arrested, local prosecutors said.

Italian media said the two face possible charges of multiple homicide and abandoning the ship before all the passengers were rescued.

The captain 'approached Giglio Island in a very awkward way, hit a rock that stuck into its left side, making (the boat) list and take on a huge amount of water in the space of two or three minutes', a prosecutor told reporters.

Island residents also said the ship was sailing far too close to Giglio and had hit an underwater rocky reef that was well known to the residents of the picturesque hilly outcrop, which has a population of just 800.

Rescuers said they plucked 100 people from the sea overnight Friday after some of the lifeboats on board failed to function or could not descend to the water from a ship that was already badly listing.

About 60 people who had not managed to escape in lifeboats were rescued from the vessel itself, including one passenger with a broken leg.

Some crew members familiar with the layout of the ship were helping divers negotiate their way around the Italian-built liner's 1,500 cabins.

Survivors from around the world - many of them with bloodshot eyes and draped in blankets in Giglio harbour - spoke on Saturday of scenes 'like the Titanic' on board and said they were not properly informed about the evacuation.

Some of the survivors were in evening wear as they had just been settling down to dinner on board when the accident happened. There were also bar and restaurant staff in crimson blazers and kitchen staff in white smocks.