The operator of a cruise ship that ran aground off Italy's west coast blamed the captain for the accident, saying on Monday his actions had caused the disaster in which at least six people died.

At a news conference in Genoa, the head of Costa Cruises, a unit of Carnival Corp, rejected suggestions that the sheer size of the cruise ship had made it impossible to evacuate the more than 4,000 people onboard safely.

These ships are ultra-safe. It is an exceptional event, which was unforeseeable, Chairman and chief executive Pier Luigi Foschi said, fighting back tears as he answered questions.

The company will be close to the captain and will provide him with all the necessary assistance, but we need to acknowledge the facts and we cannot deny human error, he said.

The 114,500-tonne Costa Concordia vessel capsized on Friday night as passengers were sitting down to dinner and now lies on its side near the port of Giglio off the Tuscan coast.

Captain Francesco Schettino was arrested on Saturday and accused of manslaughter and abandoning the ship before all of the people were evacuated. With rescue operations suspended on Monday morning, 16 people were still unaccounted for.

Foschi said the ship had deviated from the correct route when it hit rocks near the coast, tearing a large hole in the hull, and that the captain had contravened company's safety procedures.

The company disavows such behaviour, which caused the accident, he said.

Prosecutors have accused Schettino, who has worked for Costa Crociere since 2002 and was promoted to captain in 2006, of leaving the ship before the evacuation was complete.

Coastguard officials have said he had refused to return to the vessel when asked to.

Foschi said the company had not had access to internal communication records but had internal witness accounts suggesting the captain stayed on board for a long time after the accident. He said the rest of the crew behaved like heroes.

Schettino has told Italian television the ship hit rocks that were not marked on maps and were not detected by navigation systems. He said the accident occurred 300 metres from shore.

Foschi said 2,300 tonnes of fuel were aboard the vessel but that there was no sign of leakage so far, as concerns grew of an impending environmental disaster if the giant ship breaks apart.

He said removing such a big vessel from its rocky resting place would be one of the most difficult things in the world.

The priority would be to seal any holes caused by the accident, and then the ship could possibly be lifted by giant balloons and towed away.

But he said he could not rule out that the ship would have to be cut into pieces in order to be removed from the scene.

Foschi said the accident would likely hurt the cruise industry in the short-term but did not expect a lasting fallout.

We have one million loyal customers are hoping that the reputation of our company will be repaired.

(writing by Silvia Aloisi)