The 184-foot luxury yacht the Bayesian owned by British tech tycoon Mike Lynch currently lies around 50 metres down on the seabed off the coast of the Sicilian fishing village of Porticello after it sank around 5am local time on Monday.
Local reports suggest a powerful storm and waterspout tornado may have hit the vessel.
Of the 22 people on board, 12 crew and 10 passengers, 15 have been rescued.
The six missing people are Mike Lynch, his 18-year-old daughter Hanna, Jonathan Bloomer, chairman of Morgan Stanley and insurance company Hiscox, and his wife Judy, Chris Morvillo, a lawyer from Clifford Chance and his wife, Neda.
The body of a man was recovered near the yacht, believed to be that of chef Recaldo Thomas, a Canadian-Antiguan working onboard.
The survivors, including Mr Lynch’s wife, Angela Bacares, were rescued after escaping onto a lifeboat.
Vincenzo Zagarola of the Italian Coastguard said the six missing tourists were feared dead.
Asked about their likelihood of being alive, he said: “Never say never, but reasonably the answer should be not.”
Italy’s fire brigade Vigili del Fuoco said it developed a plan to enter the wreckage of Bayesian, which is resting on the seabed off the coast at a depth of 50 metres. It described the operation as “complex”, with divers limited to 12-minute underwater shifts.
Firefighter divers reached parts of the vessel through the gap, Giornale Di Sicilia reported on Tuesday, but are yet to make it to the cabins.
It’s been suggested the Bayesian sank because hatches and portholes could have been opened allowing water inside quickly when the ship capsized.