Emergency Services in Italy are denying reports that a seventh body has been found amid the wreckage of the Costa Condordia this morning.
Earlier, authorities had said 16 people were missing.
But Italian coastguard official Marco Brusco said last night that 25 passengers and four crew members were unaccounted for three days after the Costa Concordia struck a reef and capsized off the coast of the tiny island of Giglio.
He did not explain the jump in figures, but indicated 10 of the missing were Germans. Two Americans were also among the missing.
Mr Brusco said there was still "a glimmer of hope" there could be survivors on parts of the vast cruise liner that have yet to be searched. The last survivor, a crewman who had broken his leg, was rescued on Sunday.
Italy's cruise liner tragedy turned into an environmental crisis as rough seas battering the stricken mega-ship raised fears that fuel might leak into pristine waters off Tuscany that are part of a protected sanctuary for dolphins, porpoises and whales.
The ship's Italian operator accused the jailed captain of causing the wreck that left at least six dead and 29 missing, saying he made an "unapproved, unauthorised manoeuvre" to divert the vessel from its programmed course.
Waters that had remained calm for the first days of the rescue turned choppy yesterday, shifting the wreckage and raising fears that any further movement could cause some of the 500,000 gallons of fuel on board to leak into the waters off Giglio, which are popular with scuba divers and form part of the protected Tuscan archipelago. Rescue operations were suspended for several hours because of the rough seas.
Italy's environmental minister raised the alarm about a potential environmental catastrophe.
"At the moment there haven't been any fuel leaks, but we have to intervene quickly," Corrado Clini, told RAI state radio.
Even before the accident there had been mounting calls from environmentalists to restrict passage of large ships in the area.
The ship's operator, Costa Crociere SpA, has enlisted one of the world's leading salvagers, Smit of Rotterdam, Netherlands, to handle the removal of the 1,000ft cruise liner and extract the fuel safely.
Smit has a long track record of dealing with wrecks and leaks, including refloating grounded bulk carriers and securing drilling platforms in the aftermath of Hurricane Katrina.
Meanwhile, the Italian cruise operator said Captain Francesco Schettino intentionally strayed from the ship's authorised course into waters too close to the perilous reef, causing it to crash late on Friday and capsize.
The navigational version of a "fly by" was apparently made as a favour to the chief waiter who is from Giglio and whose parents live on the island, local media reported.
A judge will decide on Tuesday whether Capt Schettino should remain jailed.
"We are struck by the unscrupulousness of the reckless manoeuvre that the commander of the Costa Concordia made near the island of Giglio," prosecutor Francesco Verusio said. "It was inexcusable."
The head of the United Nations agency on maritime safety said lessons must be learned from the Concordia disaster 100 years after the Titanic rammed into an iceberg, leading to the first international convention on sea safety.
"We should seriously consider the lessons to be learned and, if necessary, re-examine the regulations on the safety of large passenger ships in the light of the findings of the casualty investigation," said Koji Sekimizu, secretary-general of the International Maritime Organisation.
Shares in Miami-based Carnival Corporation, which owns the Italian operator, slumped more than 16% yesterday.
The two missing Americans are Jerry Heil, 69, and his wife Barbara, 70, from White Bear Lake, Minnesota.
Costa Crociere chairman and chief executive Pier Luigi Foschi said the company would provide Capt Schettino with legal assistance, but he disassociated Costa from his behaviour, saying it broke all rules and regulations.
"Capt Schettino took an initiative of his own will which is contrary to our written rules of conduct," Mr Foschi said in his first public comments since the grounding.
At a news conference in Genoa, the company's home base, Mr Foschi said Costa ships' routes were programmed into their navigational systems and alarms went off when they deviated. Those alarms were disabled if the ship's course was manually altered, he said.
"This route was put in correctly upon departure from Civitavecchia," he said, referring to the port outside Rome. "The fact that it left from this course is due solely to a manoeuvre by the commander that was unapproved, unauthorised and unknown to Costa."
Foschi said only once before had the company approved a "fly by" of this sort off Giglio - last year on the night of August 9-10. In that case, the port and company had approved it.
Residents, however, said such displays have occurred several times in the past, though always in the summer when the island was full of tourists.
Mr Foschi did not respond directly to prosecutors' and passengers' accusations that Capt Schettino abandoned ship before all passengers had been evacuated, but he suggested his conduct was not as bad in the hours of the evacuation as has been portrayed. He did not elaborate.
The Italian coastguard says Capt Schettino defied their entreaties for him to return to his ship as the chaotic evacuation of the more than 4,200 people aboard was in full progress.
After the ship's tilt put many life rafts out of service, helicopters had to pluck to safety dozens of people remaining aboard, hours after Capt Schettino was seen leaving the vessel.
The captain has insisted in an interview before his jailing that he stayed with the vessel to the end.