Six people are now presumed dead after the super yacht they were onboard sank in a violent storm off the coast of Sicily.

Divers tried in vain on Tuesday to gain access to the inside of the sunken 56-metre Bayesian luxury vessel, where rescue crews believe those missing may have been trapped.

Those unaccounted for are the tech entrepreneur Mike Lynch and his teenage daughter Hannah Lynch; the Morgan Stanley International chair Jonathan Bloomer and his wife, Judy; and the Clifford Chance lawyer Chris Morvillo and his wife, Neda.

Rescuers said they were working on the assumption that the boat sank quickly after being hit by a tornadic waterspout in a storm at about 5am on Monday.

Vincenzo Zagarola of the Italian coastguard confirmed there had been no sign of the missing passengers more than 36 hours into the rescue mission.

He said: “We do not exclude that they are not inside the boat, but we know the boat sank quickly. We suppose that the six people missing may not have had time to get out.”

Asked about the likelihood of them being alive, he replied: “Never say never, but reasonably the answer should be not.”

The national director of Italy’s firefighting department divers, Giuseppe Petrone, said that his team of specialist divers had managed to locate a breach in the sailboat’s hull and were working to open a passage to reach the cabins where they hope to find the bodies of the six missing individuals.

“We have finally located a breach,” Petrone said. “Our men are working to open it.”

The divers are hampered by debris obstructing the cabin, and the need to surface after 10 minutes because the wreck lies about 150ft below the surface.

The UK’s Marine Accident Investigation Branch confirmed that four of its inspectors were being sent to Palermo.

Diving teams from the Italian firefighting service, who arrived from Rome, Sassari and Cagliari on Monday, completed a dive on Tuesday morning. Marco Tilotta, who is in charge of the firefighter-divers from Palermo, said there were numerous challenges in recovering bodies.

“The greatest challenge is the depth, which does not allow for immediate interventions. You have to consider that when we go underwater, we have three minutes to descend and eight minutes to work on the wreck. Then we have to begin the ascent phase.

“There is also the problem of accessing the vessel with all the belongings inside and the fact that the boat is positioned at 90 degrees. We have not yet entered the boat. We plan to do so soon and inspect every inch of the vessel.”

The Italian coastguard did confirm yesterday that a body recovered on Monday, was that of the vessel’s chef, Recaldo Thomas. He had dual Canadian and Antiguan citizenship and was one of 10 crew members on board.

Tilotta said that apart from that discovery, no others had been located. Fifteen people have so far been rescued, including Lynch’s wife, Angela Bacares, who owned the boat, and a one-year-old girl with her mother.

Lynch co-founded Autonomy, a software business that became one of the shining lights of the UK tech scene in the mid-90s.

Once described as Britain’s Bill Gates, Lynch spent much of the past decade in court defending his name against allegations of fraud related to the sale of Autonomy to the US tech company Hewlett-Packard for $11.1bn.

The 59-year-old was acquitted by a jury in San Francisco in June, after he had spent more than a year living effectively under house arrest.

As local people came to terms with the shock of the events of Monday, those also caught up in the storm gave information to crews at the dock in Porticello, close to where the vessel sank.

Karsten Borner, 69, the captain of a sailboat that was alongside the Bayesian, said the vessel carrying Lynch and 21 other passengers sank within minutes.

“We were also awakened by the storm,” Karsten said. “The first thing I did was to start the engines of my sailboat to give more stability to the vessel. I don’t know if the Bayesian did the same. It seems like they were also suddenly caught by the storm.

“After securing our boat, we immediately approached the Bayesian. But it had already sunk. I have never seen a vessel of this size go down so quickly. Within a few minutes, there was nothing left. Then we saw the raft with the 15 passengers. It was a tragedy.”

Fabio Cefalù, 36, a fisher from Porticello, was one of the first to attempt to help the Bayesian.

“I arrived at the port at 3.30am for a fishing trip,” he said. “But when we saw the first flashes of lightning, we decided to stop. At 3.55am, a mini tornado arrived. The docks of the port diverted it and it hit the sailboat head-on. They were in the wrong place at the wrong time.”

Cefalù said the whirlwind lasted about “10 minutes with strong winds and rain”.

He added: “We saw a flare 500 metres from the dock. We went to see what had happened. We only saw the floating debris of the boat. We immediately called the coastguard. The sea was terrible. The wind very strong. The storm destroyed my solar panels. The vessel was hit head-on. I thought I would find someone in the sea, but nothing. The boat had disappeared from the radar. In my opinion, the missing passengers are still onboard. They were caught in their sleep by the storm and didn’t have time to get out.”

Speaking to reporters, the British ambassador to Italy, Edward Llewellyn, said: “It’s a tragedy, I met with the survivors, I wanted to express my solidarity and that of the British embassy.”

Bayesian had completed a number of sailings in recent days, calling at various ports in Sicily, according to the ship-tracking website VesselFinder. The super yacht could accommodate up to 12 guests in six suites and was listed for rent for up to €195,000 (£166,000) a week. It was built in 2008 by the Italian company Perini Navi.

In a separate development on Monday, Lynch’s co-defendant at the US trial, Stephen Chamberlain, died after being hit by a car while out running in Cambridgeshire.

Chamberlain, the former vice-president of finance at Autonomy, was hit on Saturday morning and had been placed on life support. In a statement Chamberlain’s lawyer, Gary Lincenberg, said he had died after being “fatally struck” by a car while out running.

Lincenberg added: “He was a courageous man with unparalleled integrity, and we deeply miss him. He fought successfully to clear his good name, which lives on through his wonderful family.”

Chamberlain’s family described the 52-year-old in a statement as a “much-loved husband, father, son, brother and friend”.

Lynch was awarded an OBE for services to enterprise in 2006, and appointed in 2011 to the science and technology council of the then prime minister, David Cameron. He was elected as a fellow to the Royal Academy of Engineering in 2008 and the Royal Society in 2014.