The owner of the luxury liner that ran aground off the coast of Italy said its captain had made "errors of judgment" as officials warned Monday the wreck was an ecological timebomb.

The death toll from Friday's disaster rose to six with the discovery early Monday of another body, as survivors returned home with harrowing accounts of chaos after the Costa Concordia ran aground off the Tuscan coast on Friday.

Rescuers are desperately searching for about 15 people, including Italians, Americans and French nationals, still missing three days after the disaster struck near the island of Giglio.

"I am always hopeful (of finding survivors) because you never know in the labyrinth of that ship. An air pocket could have allowed people to survive a few days more," Giglio mayor Sergio Ortelli told AFP.

The vessel's captain Francesco Schettino, was arrested Saturday with first officer Ciro Ambrosio. Media reports say they could face charges of multiple homicide and abandoning ship before all thepassengers were rescued.

"It seems that the commander made errors of judgement that had serious consequences," said a statement from the liner's ownerCosta Crociere, Europe's largest cruise ship operator.

"His decisions in the management of the emergency did not follow Costa Crociere's procedures, which are in line with international standards."

The prosecutor leading the investigation, Francesco Verusio, told reporters that Schettino had left the stricken liner "well before" the last passengers were evacuated.

He said the captain had not followed the correct route and "approached Giglio island in a very clumsy manner".

Coast guard officials also said the captain ignored repeated requests from them to return to his ship as the rescue operation continued.

Island residents have already said the ship was sailing far too close to Giglio and had hit a reef well known to inhabitants.

Prosecutors have also said the crew mishandled the emergency, delaying the start of the evacuation until an hour after the accident, and survivors have spoken of scenes of utter chaos and panic on board the vast 17-deck liner.

Italian officials also warned Monday of the risk the wreck of the 114,500-tonne Concordia could pose to the pristine environment around Giglio, which lies in a marine nature reserve.

Environment Minister Corrado Clino said "urgent action" was needed as the wreck posed a serious risk to the environment.

"There have been no leaks, but this is an ecological timebomb inside the ship and it is being monitored constantly," Giglio's mayor also said, adding that there were plans to lay booms to try to contain any spill.

Rescuers said the search in the ship was highly dangerous because the decks were pitched at almost a 90-degree angle and there was a risk the ship could slip off the rocks it had struck and sink altogether.

Fire crew chief Cosimo Pulito said they would keep searching until the whole ship had been covered but the weather was deteriorating Monday, which could complicate rescue operations.

The Concordia, the flagship of Costa Crociere's fleet, was carrying more than 4,200 people when it hit the rocks before running aground on Friday the 13th, just as many passengers were settling down to dinner.

Several passengers have described confusion on board as the lights went out and how they were at first told it was just an electrical fault -- before the ship lurched sharply onto its side and panic set in.

Some have likened the disaster to the Titanic, which sank in the Atlantic with some 1,500 people on board on its maiden voyage in April 1912.

"In one corridor we smashed a window and took the life jackets," one passenger, Antonietta Simboli, told Italian newspapers. "But as there weren't a lot of them, we were stealing them from each other."

US national Amanda Warrick told CNN how the situation degenerated.

"Those were the most chaotic moments because everyone was pushing, shoving each other, trying to get on a lifeboat. It was chaos," she said.

French tourist Olivier Carrasco said he would sue the cruise operator.

"It took an hour and a half before a real alert was sent out," he told French newspaper Sud-Ouest, adding that the light on his life vest failed.

Investigators on Sunday started analysing a "black box" recovered by rescuers, which logged the 291-metre long ship's movements and conversations between personnel.

The people on board included some 60 nationalities, although nearly a third of the passengers were Italians, followed by Germans and French.

On Sunday, emergency teams rescued two South Korean honeymooners and an Italian crewman suffering a broken leg.

But the bodies of a Spanish man and an Italian were also discovered on Sunday in the submerged part of the vessel, after the deaths of two French passengers and a Peruvian crew member were confirmed on Saturday.

Medical sources said around 60 people had been injured, two seriously.

The honeymooners, Han Ki-Deok and his wife Jeong Hye-Jin, both 29-year-old schoolteachers, told South Korea's Yonhap news agency that they had been sleeping after dinner, oblivious to the disaster outside.

"By the time we woke up, the ship was tilting," Yonhap quoted Han as saying.

The pair stayed in their dark cabin with no power, subsisting on bits of cookie and water and shouting for help until they were hoarse.

The disaster happened just hours after the ship had left the port of Civitavecchia near Rome -- and before passengers had had time to take part in the ship's emergency drill.