One man has died and six people are missing after a luxury yacht was struck by an unexpectedly violent storm and sank off the Sicilian capital Palermo, the Italian coast guard says.

British tech entrepreneur Mike Lynch was among the missing, a person familiar with the rescue operation said.

The 56-metre-long (184-ft) sailboat was identified as the British-registered Bayesian and sank with 22 people on board shortly before sunrise, the coast guard said.

British tech entrepreneur Mike Lynch is reportedly among the missing. – WikiCommons

The missing people were of British, American and Canadian nationality, the coast guard said. The 15 people rescued included a one-year-old child.

One of the survivors, identified only as Charlotte, said she had momentarily lost hold of her 1-year-old daughter Sofia in the water, but then managed to hold her up over the waves until a lifeboat inflated and they were both pulled to safety, Italian news agency ANSA reported, quoting the mother.

"The wind was very strong. Bad weather was expected, but not of this magnitude," a coast guard official in Palermo said.

Storms and heavy rainfall have swept down Italy in recent days – with floods and landslides causing major damage in the north of the country – after weeks of scorching heat.

Eight of those rescued were transferred to local hospitals. All were in stable condition, local media reported.

Karsten Borner, the captain of a ship who rescued survivors describes moment of luxury yacht sinking. – Reuters

The captain of a nearby boat said that when the storm hit he turned the engine on to keep control of the vessel and avoid a collision with the Bayesian.

"We managed to keep the ship in position and after the storm was over, we noticed that the ship behind us was gone," Karsten Borner said.

"I figured it was a strong hurricane gust. Very strong. Very strong.

"And we have also been heeling a lot but the other ship … They went flat on the water and then down."

"There was a light and we saw that the ship was aside and then we saw a triangle. So I think she went back down."

He said that his crew then found some of the survivors on a life raft, including three who were seriously injured and took them on board before the coast guard picked them up.

Borner said "a little baby and the wife of the owner" were among the survivors, while the owner of the sunken ship and another child were among those missing.

Divers and helicopters search Palermo waters for missing yacht passengers. – Reuters

Local fisherman Francesco Cefalu’ said he had seen a flare from shore at around 4.30am and immediately set out to the site but by the time he got there, the Bayesian had already sunk, with only cushions, wood and other items from the superyacht floating in the water.

“But for the rest, we didn’t find anyone,” he said from the port hours later.

He said that he immediately alerted the coast guard and stayed on site for three hours, but didn't find any survivors.

”I think they are inside, all the missing people.”

He said he had been up so early to check the weather to see if he could go fishing, and surmised that a sudden waterspout had struck the yacht.

“It could be that the mast broke, or the anchor at the prow pulled it, I don’t know,” he said.

The coast guard said the boat had been found at a depth of 49 metres and that divers were inspecting the wreck.

Prosecutors in the nearby town of Termini Imerese have opened an investigation to look into what had gone wrong.

The Bayesian was built by Italian shipbuilder Perini in 2008 and was last refitted in 2020, and was managed by yachting company Camper & Nicholsons.

The Bayesian, left, and the Duch sailboat Sir Robert Baden Powell at anchor off the Sicilian village of Porticello the night before the storm. – AP 

It won a string of awards for its design and can accommodate up to 12 guests in six suites and a crew of 10, according to online specialist yacht sites.

Online charter sites list it for rent for up to €195,000 (about US$215,000) a week.

Formerly know as Salute, or health in Italian, its 75-metre mast is the tallest aluminium mast in the world, Perini said on its website.

The boat left the Sicilian port of Milazzo on August 14 and was last tracked east of Palermo on Sunday evening, with a navigation status of "at anchor", according to vessel tracking app Vesselfinder.

A UK foreign ministry spokesperson said British officials were in contact with local authorities over the incident and were ready to provide consular support for Britons who were affected.

Storm that caused yacht to sink is seen sweeping through Palermo street. – Reuters