British tech tycoon Mike Lynch, dubbed the 'British Bill Gates', is among five others who are believed to be trapped inside a luxury yacht in Sicily.
The boat carrying 22 passengers and crew sank at around 5am local time on Monday (19 August).
CCTV footage below shows a clip of the Bayesian superyacht moments before it 'vanished in 60 seconds'.
Mr Lynch, along with his daughter Hannah Lynch, Morgan Stanley International bank chairman Jonathan Bloomer, his wife Judy Bloomer, Clifford Chance lawyer Chris Morvillo and his wife Neda Morvillo have been named as missing.
The businessman who founded software company Autonomy in 1996 was cleared of conducting fraud to an $11 billion (£8.64 billion) sale to US firm Hewlett Packard.
According to reports, the vessel was around half-a-mile off the coast of Porticello when it sank.
Fifteen people onboard, including Mr Lynch’s wife, Angela Bacares, were rescued after escaping onto a lifeboat. The ship's chef has been found dead.
Vincenzo Zagarola, of the Italian Coastguard, told PA news agency: “We think they are still inside the boat, that is our very hard idea.
“Our search and rescue activity by sea and air has gone on for around 36 hours.
“Of course, 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 of the boat.”
On the chances of the six being alive, he added: “Never say never, but reasonably the answer should be not.”
Italy’s fire brigade Vigili del Fuoco has referred to the search operation as 'complex' with underwater divers taking 12-minute shifts.
In regards to the CCTV footage, Giornale di Sicilia explained: "In just sixty seconds - says the owner of the villa - you can see the ship disappear.
"Of about twenty cameras installed in the house, only one was not disturbed by the wind and rain. You can clearly see what is happening.
"There was nothing that could be done for the boat. It disappeared in a very short time."
Meanwhile, a spokesperson for the UK Foreign, Commonwealth and Development Office (FCDO) said: "We are in contact with the local authorities following an incident in Sicily, and stand ready to provide consular support to British nationals affected."
A spokeswoman for Clifford Chance also said: “We are in shock and deeply saddened by this tragic incident.
“Our thoughts are with our partner, Christopher Morvillo, and his wife Neda who are among the missing.
“Our utmost priority is providing support to the family as well as our colleague Ayla Ronald, who together with her partner, thankfully survived the incident.
“Our thoughts extend to the other passengers and crew, and all those affected.
“We have no further comment at this time. We, and the families, ask that their request for privacy is honoured during this period.”
Topics: World News, Bayesian yacht
Anish Vij