The 184-foot luxury yacht Bayesian, owned by British technology tycoon Mike Lynch, is currently around 50 meters deep on the seabed off the coast of the Sicilian fishing village of Porticello after it sank at around 5 a.m. local time on Monday.
Local reports suggest a severe storm and tornado may have hit the ship.
Of the 22 people on board, 12 crew and 10 passengers, 15 were rescued.
The six missing people are Mike Lynch, his 18-year-old daughter Hanna, Jonathan Bloomer, chairman of Morgan Stanley and the insurance company Hiscox, and his wife Judy, Chris Morvillo, a lawyer for Clifford Chance, and his wife, Neda.
The body of a man was recovered near the yacht, believed to be that of chef Recaldo Thomas, an Antiguan-Canadian who worked on board.
The survivors, including Mr Lynch’s wife Angela Bacares, were rescued after escaping in a lifeboat.
Vincenzo Zagarola of the Italian Coast Guard said the six missing tourists were suspected of being dead.
Asked about the likelihood of them being alive, he said: “Never say never, but the reasonable answer would be no.”
Italy’s Vigili del Fuoco fire brigade said it had developed a plan to enter the wreckage of the Bayesian, which is resting on the seabed off the coast at a depth of 50 meters. It described the operation as “complex”, with divers limited to 12-minute underwater shifts.
Firefighting divers have reached parts of the ship through the opening, Giornale Di Sicilia reported on Tuesday, but have not yet been able to reach the cabins.
It has been suggested that the Bayesian sank because hatches and portholes could have been opened, allowing water to quickly enter as the ship capsized.