Fears are growing for the 29 people still missing from a shipwreck off Italy, four days after the vessel crashed.

The Italian coastguard said 25 passengers and four crew members remained unaccounted for after the Costa Concordia ran into a reef off the Tuscan coast near the island of Giglio on Friday.

Six people have been confirmed dead and officials last night revised the number of those missing up from an estimated 16 people.

At least three Italian families have said that although their loved ones were listed among those safely evacuated, they had not heard from them. About 10 Germans and two Americans were thought to be among those unaccounted for.

Coastguard official Marco Brusco said he held a ''glimmer of hope'' that some of the missing might have survived, but Giglio mayor Sergio Ortelli said earlier that hopes of finding any of them alive were minimal.

He told the Italian press that the only hope was that bubbles of air had formed within the ship after it hit the rocks.

Meanwhile, the tragedy could also become an environmental crisis as rough seas battering the ship have raised fears fuel might leak into waters that are part of a protected sanctuary for dolphins, porpoises and whales.

The operators of the cruise liner have blamed the captain for sailing close to land to ''show the ship to the port''.

The chairman of Costa Cruises said the unauthorised deviation from the route had been taken to ''make a salute''.

Pier Luigi Foschi has apologised for the tragedy which has left dozens of people injured and the 114,000-tonne Costa Concordia lying on its side off Tuscany.

At the centre of the investigation into the disaster is the liner's captain, Francesco Schettino, who is being investigated by prosecutors for possible manslaughter, abandoning ship and causing a shipwreck.

He has been accused of leaving the vessel before ensuring that all of the 4,200 people aboard, including 35 Britons, were safely evacuated.

Capt Schettino insisted in an interview before his jailing that he stayed with the vessel to the end however.

Clarence Mitchell, who is representing Costa Cruises, said: ''Mr Foschi confirmed the captain had been approaching the island of Giglio to 'make a salute'.

''The company says this (incident) was caused by an attempt by the captain to show the ship to the port.

''But there's a criminal investigation going on and we're not going to say anything that's going to compromise that or the captain's case.''

A judge will decide today whether Capt Schettino should stay in jail.

Prosecutor Francesco Verusio slammed the captain's alleged conduct as ''inexcusable.''

He told reporters: ''We are struck by the unscrupulousness of the reckless manoeuvre that the commander of the Costa Concordia made near the island of Giglio.''

As British survivors told of the panic on board after the ship began to list, Mr Foschi said the liner had passed all safety and technical tests in its 2011 evaluation.

Explaining that the ship was ''ultra safe'', he said the captain had made an unauthorised and unapproved deviation from the ship's programmed course.

''This route was put in correctly,'' he said. ''The fact that it left from this course is due solely to a manoeuvre by the commander that was unapproved, unauthorised and unknown to Costa.''

Mr Foschi added: ''Personally and on behalf of the Costa Crociere (Cruises) I want to say we are very sorry for this tragic accident that's happened.''

Capt Schettino, who has commanded the ship since it was built in 2006, has said he is not to blame and that nautical charts did not show the rocks off the tiny island of Giglio.

Among the British survivors was James Thomas, 19, from Sutton Coldfield, Birmingham, a dancer who helped direct petrified passengers off the vessel.

He said people on board ''knew something was deadly wrong'' when the ship began to tilt, adding that the instruction to abandon ship should have been given ''an hour earlier, if not more''.

He went on: ''We knew we were going to have to do something drastic to get out of the situation we were in. Even if it was 'just in case' it (the call to abandon ship) should have been called an hour earlier, if not more.''

Mr Thomas added: ''I saw people with some horrific injuries and that is one thing which I am never going to be able to get out of my head, which is the worst thing.''

Another survivor, Rose Metcalf, 23, from Wimborne in Dorset, said: ''There was absolute panic. It was just terrifying, it was a case of just trying to keep people calm. People were white, people were crying, screaming.''

The body of a sixth victim of the tragedy was found on the ship yesterday.

The search for any survivors continued until it had to be suspended in early afternoon after the vessel shifted a few inches in rough seas.

Later, with the weather improving, the search resumed.

Costa Cruises was concerned about the 500,000 gallons of fuel on board which are in 17 separate tanks.

It is feared that any further movement of the ship could cause some of it to leak into the water.