Italian divers have retrieved the body of Mike Lynch's 18-year-old daughter, Hannah Lynch, who was the sole victim unaccounted for after the British tech magnate's family luxury yacht sank this week off Sicily.

The British-flagged Bayesian, a 184-feet-long luxury sail boat carrying 22 passengers and crew, was anchored off the port of Porticello, near Palermo, when it capsized and rapidly sank after being struck by a pre-dawn storm on Monday.

Hannah Lynch's body was discovered on Friday by specialist divers who have been scouring the submerged vessel for the past five days, said a senior official with knowledge of the rescue operation said, declining to be named. The woman's body was found on Friday, the Italian Coast Guard told the Associated Press.

The wreck is lying at a depth of 50 meters and once inside the passageways are narrow. The fire brigade on Friday described rescue operations as "long and delicate," and said they involved more than 400 people, including 28 specialist divers.

The bodies of the other five dead passengers, including Mike Lynch, were recovered on Wednesday and Thursday from inside the yacht. Those that died included: Judy and Jonathan Bloomer, a non-executive chair of Morgan Stanley International; and Clifford Chance lawyer Chris Morvillo, an American citizen, and his wife, Neda Morvillo.

The body of the only crew member who died, onboard chef Recaldo Thomas, was found near the wreck on Monday.

Official identification of the corpses and autopsies will take place in Palermo.

"The Lynch family is devastated, in shock and is being comforted and supported by family and friends," Lynch's family said in a statement on Friday.

"Their thoughts are with everyone affected by the tragedy. They would like to sincerely thank the Italian coastguard, emergency services and all those who helped in the rescue."

"Their one request now is that their privacy be respected at this time of unspeakable grief."

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A judicial investigation has been opened into the sinking, which has baffled naval marine experts who say a boat like the Bayesian, built by Italian high-end yacht manufacturer Perini, should have withstood the storm.

The yacht's captain James Cutfield, his eight surviving crew members and passengers have been questioned by police, but have not made public comments. Investigating prosecutors are due to hold a press conference on Saturday.

Complex Salvage Operation

Giovanni Costantino, CEO of The Italian Sea Group, which owns Perini, told Reuters the shipwreck was the result of a string of "indescribable, unreasonable errors" made by the crew, and ruled out any design or construction failings.

Pulling the wreck out of the sea, where it is now lying on its right side, apparently intact, may help investigators determine what happened, but the operation is likely to be complex and costly.

Nick Sloane, a South African engineer who led the operation to salvage the Costa Concordia cruise liner that sank in 2012, said in Italian media interviews on Friday that the operation would cost up to 15 million euros ($16.7 million).

He told daily La Repubblica that salvaging the yacht would take six to eight weeks, including preparation work, and would have to be completed by mid-October, without specifying the reasons for the timing.

Bringing the yacht to the surface will have to be done "very, very slowly", and might take a couple of days, he said.