The captain of a cruise ship that ran aground off Italy's Tuscan coast, killing at least six people, made an "unauthorized" deviation from the liner's programmed course, the cruise company's chief executive said Monday.

Also Monday, Italian coast guard officials raised the number of missing people after the shipwreck to 29 from an earlier estimate of 16.

Italian Coast Guard official, Marco Brusco, said the missing include 25 passengers and four crew members. He said 10 Germans and two Americans are unaccounted for three days after the ship hit a reef.

Rescue operations were suspended briefly as the wrecked ship, perched on its side, partially submerged in the waters near the island of Giglio, shifted about nine centimetres in choppy seas.

Alfio Pini, the fire chief, said rescue operations resumed after the waters calmed, adding that they would continue as long as safety permitted and there was hope of finding people alive.

Costa Crociere chairman and CEO Pier Luigi Foschi said the company stood by the captain, Francesco Schettino, and would provide him with legal assistance. But he told reporters that the company, which is owned by the world's largest cruise line, Carnival Corp., dissociated itself from his behaviour.

He said the routes of Costa ships are programmed, and alarms go off when a vessel deviates from the correct course.

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

12 Canadians escape safely

The Costa Concordia ran into a reef Friday night and capsized into the port area of Giglio, sparking a frantic evacuation of the ship, which carried 4,200 passengers and crew. There were 12 Canadian tourists known to be on board, and all got off the ship unscathed.

Coast guard officials have expressed concern the ship might slip off the rocks where it is now perched.

Italy's Environment Minister Corrado Clini said Monday that he plans to declare a state emergency over the capsized ship, which would free up state funds to prevent an environmental disaster.

The fear is that if the ship shifts significantly, some 1.9 million litres of fuel may begin to leak into the pristine waters. A Dutch firm has been called in to help extract the fuel.

'The environmental risk for the island of Giglio is extremely high.'— Italian Environment Minister Corrado Clini

Environmental officials said some liquid has been released into the water, but it is not known whether it is fuel.

"The environmental risk for the island of Giglio is extremely high," Clini said, according to the news agency ANSA. "The goal is to avoid that the fuel leaks from the ship. We are working on this. The intervention is urgent."

Protective barriers have been put in place just in case.

Costa Concordia passed 2011 safety and technical tests

The Costa CEO told the news conference Monday that the liner had passed all safety and technical tests in its 2011 evaluation. He said the company's main concern was the safety and well-being of the passengers and crew.

The cruise ship Costa Concordia leans on its side Sunday, after it ran aground off the tiny Tuscan island of Giglio, Italy. (Gregorio Borgia/Associated Press)

Italian rescue officials said a passenger's body had been found in the wreckage, raising to six the number of confirmed dead.

Fire official Luca Cari told state radio Monday that the victim was a man, found in a corridor in the part of the ship that was still above water. He said the victim was wearing the orange life-vest used by passengers.

Onshore, attention has focused on the captain, Schettino, who was spotted by coast guard officials and passengers fleeing the sinking ship while the chaotic and terrifying evacuation was underway.

Authorities were holding Schettino for suspected manslaughter, and a prosecutor confirmed Sunday they were also investigating allegations the captain abandoned the stricken liner before all the passengers had escaped.

Carnival Cruises takes financial hit

According to the Italian navigation code, a captain who abandons a ship in danger can face up to 12 years in prison.

Passengers aboard the stricken luxury liner said the ship's crew was ill-prepared to handle the emergency.

Meanwhile, Costa's parent company, Carnival Cruises, took a financial hit Monday, with shares falling as much as 17 per cent on the London Stock Exchange.

The company said in a statement that the ship was expected to be out of service for the rest of the fiscal year, costing Carnival $85 million to $95 million.

"At this time, our priority is the safety of our passengers and crew,” Micky Arison, Carnival's chairman and CEO, said in a statement. “We are deeply saddened by this tragic event and our hearts go out to everyone affected by the grounding of the Costa Concordia and especially to the families and loved ones of those who lost their lives."

With files from The Associated Press