Italian rescuers on Monday searched the wreck of a stricken luxury liner three days after it crashed on the shores of Tuscany as the number missing was revised upward to 29.

The head of the Italian coastguard, Marco Brusco, said ‘a glimmer of hope remains’ of finding survivors and that fire brigade crews would work on the ship through the night in their increasingly desperate search.

He said four crew members and 25 tourists including six Italians remained unaccounted for, revising sharply upward an earlier estimate of 15.

"It's dangerous work," he said, as divers and mountain rescue teams spoke of the difficulties of operating in the half-submerged ship.

The earlier figure for the missing did not take into account at least 10 Germans that a German official said were unaccounted for Monday. American and French tourists are also among the missing, as well as crewmen.

The death toll also rose to six after divers found the body of a man in the early hours of Monday.

Three of the victims – two Frenchmen and one Peruvian crew member – drowned after jumping into the chilly Mediterranean waters along with dozens of others in a chaotic evacuation in the Friday the 13th tragedy.

Rodolfo Raiteri, head of the coastguard's diving team, told the media on the shore: "The conditions inside are disastrous. It's very difficult. The corridors are cluttered and it's hard for the divers to swim through."

But the local mayor also voiced hope of finding more people alive.

"You never know in the labyrinth of that ship. An air pocket could have allowed people to survive a few days," mayor Sergio Ortelli told the media.

Choppy seas forced a temporary evacuation of the stricken 17-deck Costa Concordia for several hours after the half-submerged ship slipped on a rocky shelf under the sea, sparking fears that the giant hulk could sink entirely.

Ortelli warned that the stricken vessel, which hit rocks and keeled over off Giglio Island, was an ‘ecological timebomb’ in the pristine waters of a marine nature reserve.

Environment Minister Corrado Clini said a state of emergency would be declared this week to drum up funds and beef up rescue and clean-up operations in case of an environmental disaster.

Captain needs

The head of the company that owns the vessel said it had hit a rock as a result of an ‘inexplicable’ error by the captain, Francesco Schettino, who was arrested on Saturday along with first officer Ciro Ambrosio.

"He carried out a manoeuvre which had not been approved by us and we disassociate ourselves from such behaviour," said Pier Luigi Foschi, the boss of Costa Crociere, Europe's largest cruise operator.

But Foschi also paid tribute to the other crew members, saying they had ‘all behaved like heroes’.

Schettino was under special surveillance in Grosseto, the main town in the area.

"He has not shown any suicidal tendencies but it is clear that he is going through a very delicate period which requires special attention," a prison official said.

Italian prosecutors accuse the two officers of multiple homicide and abandoning ship before all the passengers were rescued.

A transcript of a conversation between Schettino and a port official was released on Monday showing that the captain refused to return to the ship to oversee rescue operations.

"Now you go to the bow, you climb up the emergency ladder and coordinate the evacuation," the official tells Schettino, according to the transcript of the conversation recorded on one of the ship's ‘black boxes’ recovered by rescuers.

"You must tell us how many people, children, women and passengers are there and the exact number of each category," he said.

"What are you doing? Are you abandoning the rescue? Captain, this is an order, I am the one in charge now. You have declared abandoning ship," the port official said.

Investigators on Sunday also started analysing the ‘black box’ for precise details of the ship's movements.