The body of British tech magnate Mike Lynch was retrieved on Thursday from the wreck of his family yacht that sank earlier this week off the coast Sicily during a violent tempest, a source close to the rescue operation said.

Lynch’s 18-year daughter Hannah is still unaccounted for, the source said. The bodies of the other four people who vanished when the boat went down were recovered from the yacht on Wednesday.

The British-flagged Bayesian, a 56-metre-long (184-ft) superyacht carrying 22 passengers and crew, was anchored off the port of Porticello, near Palermo, when it disappeared beneath the waves in a matter of minutes after a fierce storm struck.

Lynch, 59, was one of Britain’s best-known tech entrepreneurs and had invited friends to join him on the yacht to celebrate his recent acquittal in a major US fraud trial.

Besides Lynch and his daughter, the other people who failed to escape from the boat were Judy and Jonathan Bloomer, a non-executive chair of Morgan Stanley International; and Clifford Chance lawyer Chris Morvillo and his wife, Neda Morvillo.

Fifteen people, including Lynch’s wife, managed to get to safety, while the body of the onboard chef, Canadian-Antiguan national Recaldo Thomas, was found near the wreck hours after the disaster.

Specialist rescuers have been searching inside the hull of the sunken yacht for the past three days, but operations have been challenging due to the depth and the narrowness of the places that the divers are scouring, the fire brigade said.

It compared the efforts to those carried out, on a larger scale, for the Costa Concordia, the luxury cruise liner that capsized off the Italian island of Giglio in January 2012, killing 32 people.

The disaster has baffled naval marine experts who said such a vessel, built by Italian high-end yacht manufacturer Perini and presumed to have top-class fittings and safety features, should have been able to withstand such weather.

Prosecutors in the nearby town of Termini Imerese have opened an investigation and authorities have started questioning passengers and witnesses.

The captain, James Cutfield, and crew have made no official comment on the disaster.

Giovanni Costantino, CEO of the Italian Sea Group , which includes Perini, said the Bayesian was “one of the safest boats in the world” and basically unsinkable.

He added that he believed the disaster was caused by a chain of human mistakes and that the storm had been expected, in interviews with Italian media.

“The ship sank because it took on water, from where investigators will have to say,” Costantino told television news programme TG1 late on Wednesday.

Citing data from the yacht’s automatic tracking system and based on available footage, Costantino said it took 16 minutes from when the wind began buffeting the yacht, and it began taking on water, for it to sink.

Costantino said the Milan-listed group had suffered “enormous damage” to its reputation, with shares falling 2.5 per cent since the disaster.