The owners of the stricken cruise ship Costa Concordia admitted yesterday that the captain had been sailing too close to rocks in order to "put on a salute" for people on the shore. Other reports suggested the captain was also giving the head waiter a better view of his home.

That version of events was further supported when it emerged that the waiter's sister had excitedly told her friends about the display in advance on Facebook. "The Concordia ship will pass very close," she wrote. "A big greeting to my brother."

The news came as the spotlight also fell on the competence of the ongoing rescue operation and the ship's records. The coastguard increased the number of people missing from 16 to 29 without explanation. Three Italian families claimed their loved ones had been listed as evacuated but had not been in contact. A sixth body was discovered as the search for a further 25 missing passengers and four crewmen continued into the night, three days after the incident.

There were also mounting concerns that an environmental disaster could compound the tragedy, with Italian authorities preparing to declare a state of emergency.

The claims that Captain Francesco Schettino deliberately sailed closer than usual to a Tuscan island on Friday after summoning the ship's head waiter to the bridge before the ship struck a reef are under investigation. Witnesses said Antonello Tievoli told the captain to be careful and warned him he was "extremely close to the shore" of his native Giglio, where the vessel has previously performed a "sail-past" with its horn blasting and lights blazing.

Mr Schettino is under arrest on suspicion of multiple manslaughter and abandoning his ship. Clarence Mitchell, who is representing the ship's owners, Costa Crociere, confirmed the captain had been approaching the island to "make a salute". He said: "The company says this 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."

The company had already blamed "human error" for the disaster involving 4,200 passengers and crew, including 35 Britons, which may become the biggest insurance loss in maritime history.

Prosecutor Francesco Verusio said the captain's actions were "inexcusable", describing the final tack as "unscrupulous and reckless". A judge will decide today whether to charge the captain.

Rescuers were forced to temporarily abandon their hunt for survivors when the 114,500-tonne ship began sliding in heavy seas. The weather is expected to worsen in the coming days and hopes of finding anyone alive are diminishing. Divers will probe the submerged part of the ship in the slim hope some people may be sheltering in air pockets.

Half a million gallons of heavy fuel oil are leaking into the pristine waters of a dolphin sanctuary. Italy's Environment Minister Corrado Clini said the risk of an ecological disaster was now "very, very high". The Concordia had just left port with 2,300 tonnes of oil on board. The International Maritime Organisation said regulations on the safety of large passenger ships could be reviewed pending the results of investigations. Images of the overturned cruiser and horror stories of terrified passengers struggling to find lifeboats in the dark could have a serious impact on the £34bn cruising industry.

Shares in Carnival, the London and Miami-based owners of Costa Crociere, slumped. Lost revenues are expected to top £62m this year with one analyst suggesting the final cost to Carnival, which operates 101 vessels, could be up to £652m. The tragedy occurred during the traditional post-Christmas boost to bookings. But the industry was at pains to point out that the 10-fold growth in passenger numbers since the 1970s was unlikely to be stemmed in the long term with three even bigger ships due to be launched this year.

Q&A: The cruise disaster

Q Why did the Costa Concordia approach within 200 metres of the shore?

A Statements from crew members and local officials suggest the unofficial approach by the vessel's captain, Francesco Schettino, pictured, was to please tourists, crew members and even Giglio locals.

Q Why did the Costa Concordia's officers take so long to sound the alarm?

A Reports have emerged of Italian passengers aboard the vessel calling Italian police with their mobile phones, while the ship's authorities sought to assure passengers the vessel was suffering only "electrical problems". Given the disastrous size of the ship's impact with the rocks and the rate at which it began listing, the ship's captain might find this question hard to answer.

Q How inept was the rescue effort and the evacuation procedure?

A The ship's crew and the owners of the vessel have been attacked for chaotic scenes and lack of advice and preparedness. But Pier Luigi Foschi, the head of the vessel's operator, Costa Crociere, noted yesterday that 20 or fewer deaths following the emergency evacuation of more than 4,000 people into cold seas, suggested procedures worked fairly well.

Q Are any more of the missing people likely to be found alive?

A With so much time – 72 hours – having passed, in such cold conditions, and with no sounds coming from inside the capsized vessel, this now appears unlikely.

Q Will emergency services be able to stop the Costa Concordia's 2,000-tonne fuel consignment from leaking into the sea?

A Last night, authorities were putting a brave face on their fight to stop an eco-disaster. Without going into details, they insisted diving crews had made progress in securing the fuel tanks before removing the diesel oil they contain. However, small amounts of oil began to appear near the vessel by yesterday afternoon.