TERMINI IMERESE: An Italian prosecutor has opened a manslaughter investigation into the deaths of British tech magnate Mike Lynch and six other people who were killed when a luxury yacht sank off Sicily this week.

The head of the public prosecutor's office of Termini Imerese, Ambrogio Cartosio, announced the investigation at a news conference, saying the probe was so far not aimed at any individual person.

Lynch's 18-year-old daughter, Hannah, was also among those who died when the family's 56-metre-long (184-foot) boat, the Bayesian, capsised during a fierce, pre-dawn storm on Monday off Porticello, near Palermo.

Fifteen people survived, including Lynch's wife, whose company owned the Bayesian, and the yacht's captain.

The captain James Cutfield and the other survivors have been questioned this week by authorities. None of them have commented publicly on how the ship went down.

Raffaele Cammarano, another prosecutor speaking at the same news conference, said that when authorities questioned Cutfield he had been "extremely cooperative".

Pulling the Bayesian out of the sea may help investigators determine what happened, but the operation is likely to be complex and costly. The wreck is lying apparently intact on its side at a depth of 50 metres (164 feet).

"It's in the interests of the owners and managers of the ship to salvage it," Cartosio said, adding "they have assured their full cooperation".

He said there was no legal obligation for the captain, crew and passengers to remain in Italy but authorities expected them to cooperate with the probe.

The sinking has puzzled naval marine experts who say a boat like the Bayesian, built by Italian high-end yacht manufacturer Perini, should have withstood the storm and in any case should not have sunk as quickly as it did.

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