Italian prosecutors have opened a manslaughter investigation over the sinking of Mike Lynch's family superyacht Bayesian off the Sicily coast on Monday.

The public prosecutor's office of Termini Imerese, headed by Ambrogio Cartosio, announced the investigation, saying the probe was not aimed at any individual person.

He said that while the yacht had been hit by a sudden meteorological event, it was "plausible" that crimes of multiple manslaughter and causing a shipwreck through negligence had been committed.

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

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

The bodies of the ship passengers were all discovered by divers on the left-hand side of the boat. 

They may have been trying to search for remaining bubbles of air, head of Palermo's Fire Brigade, Girolamo Bentivoglio Fiandra, said.

It comes one day after the body of Mike Lynch's 18-year-old daughter Hannah was recovered from the site of the shipwreck.

She was the last person unaccounted-for after the tragedy, with the body of Mr Lynch and four others recovered by rescue divers on Thursday.

Officials did not confirm the identities of the other bodies recovered from the water.

Others reported missing from the yacht include the chairman of Morgan Stanley International, Jonathan Bloomer, Mr Bloomer's wife Judy, Clifford Chance lawyer Chris Morvillo and his wife, Neda Morvillo.

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

Fifteen of the 22 people onboard survived the shipwreck, including Mr Lynch's wife, whose company owned the Bayesian, and the yacht's captain.

Angela Bacares, Charlotte Golunski and her one-year-old daughter, Sofia, also survived.

The boat's maker has since blamed the shipwreck on "indescribable, unreasonable errors" by the crew.

Giovanni Costantino, CEO of the superyacht's manufacturing company Italian Sea Group, said there were no structural problems with the vessel that could have led to the shipwreck, arguing the crew were ill-prepared.

"It had absolutely no problem, it was a model for so many ships because it was so stable," he told the BBC.

"The weather alerts clearly showed the storm would have arrived at 4am, the captain should have closed every hatch, raised anchor, sailed into the wind, and lowered the keel. Then everyone could have gone back to sleep and the cruise would have happily continued."

Mr Costantino told Reuters correct emergency procedures had not been followed despite stormy weather already being forecast.

"The boat suffered a series of indescribable, unreasonable errors, the impossible happened on that boat … but it went down because it took on water. From where, the investigators will tell."

The Bayesian, a 56-metre British-flagged yacht, went down in a storm early on Monday as it was moored about a kilometre offshore.

Another yacht anchored near the Bayesian escaped unharmed.

While it was initially believed a water spout had caused the superyacht to sink, it was most likely a "downburst", Mr Cammarano said. 

A downburst is a very strong downward wind that is an intense but relatively frequent event at sea.

Mr Cammarano said it was likely the passengers were unable to escape the vessel because they were asleep when the storm struck. 

Drug and alcohol tests were not carried out on the survivors as they were in a state of shock and needed treatments for injuries.

ABC/Wires