At least one person was killed and six others, including a British software mogul, were missing on Monday after a sailing yacht carrying 22 people sank during a violent storm off the coast of Sicily, Italian officials said.

The yacht sank after a storm “with strong winds” struck around 5 a.m., according to Luciano Pischedda, the Italian Coast Guard official overseeing the rescue operations. The vessel had been anchored about a half-mile off Porticello, about 12 miles east of the Sicilian capital, Palermo.

Camper & Nicholsons, managers of the sailing yacht, said in an emailed statement that there were 12 guests and 10 crew onboard.

The authorities have yet to determine what caused the yacht to sink. “This will be ascertained later,” Mr. Pischedda said, adding that several crew members were in the hospital and had not spoken to investigators.

Among the dead and missing, four were British, two were American, and one was a man with dual citizenship from Canada and Antigua, he said.

One of those unaccounted for is Mike Lynch, a British software mogul who was acquitted in the United States in June of fraud, according to a person with knowledge of the matter who spoke on the condition of anonymity because they were not authorized to speak publicly about it.

His wife, Angela Bacares, was rescued. Mr. Lynch, who once was described as Britain’s Bill Gates, had fought for more than a decade against accusations that he had defrauded Hewlett-Packard when he sold it his company, Autonomy, for $11 billion. The legal battle represented one of the biggest fraud cases in Silicon Valley history.

Salvatore Cocina, a top official with Sicily’s civil protection agency, said that Mr. Lynch’s daughter, Hannah Lynch, was also among the six people missing. All were passengers on the yacht, the Coast Guard said.

Mr. Cocina said the body that had been recovered was that of the yacht’s cook.

A passenger ship sailing under the flag of the Netherlands, the Sir Robert Baden Powell, anchored nearby, provided immediate assistance to the 15 surviving passengers, Mr. Pischedda said.

Karsten Börner, the captain of the Sir Robert, said in a telephone interview said he had to steady his ship to “keep it in position” during what he described as very strong winds. During the storm, the yacht seemed to disappear, he said. “At a certain moment she was gone behind us,” he said.

After the wind dropped down, “we couldn’t see the yacht any more, and then we saw a red flare,” he added. When he and a colleague went to check out the flare’s position, they spotted a “life raft adrift with 15 people on board, one of them a baby and four people injured,” he said. They were taken aboard the Sir Robert and Captain Börner contacted the Coast Guard, which brought the survivors to shore.

Captain Börner said he didn’t know when the ship went down because the storm made it difficult to see clearly. The wind was “really violent,” he said.

For the most part, the survivors didn’t speak much he said. “They were all under shock,” he said. “It was a bad, bad situation.”

Monday’s storm surprised experts with its intensity.

Col. Attilio Di Diodato, director of the Italian Air Force’s Center for Aerospace Meteorology and Climatology, said the agency had registered intense lighting activity and strong gusts of wind in the area at the time of the accident.

“It was very intense and brief in duration,” he said of the storm. He could not rule out that it had been a waterspout, or small tornado, but nevertheless called it “an important event.”

Italy’s firefighter corps said that its divers had started carrying out a search and rescue mission at dawn.

On Monday afternoon, expert divers with the firefighter corps arrived in Porticello to search the sunken vessel, which was under about 165 feet of water.

Operations at that depth, were “complicated,” and required specialized divers, said Luca Cari, a spokesman for the firefighters.

Fabio Cefalù, a fisherman in Porticello, told the Italian newspaper La Repubblica that he saw a waterspout — a sort of mini-tornado — that lasted “about 12 minutes” off the shore of Porticello shortly before 4 a.m.

Around 4:10, he said he saw a red flare go off “about 500 meters from the shore.” He said he waited for the weather to calm down, and went out about 20 minutes later to the site where the flare had gone off.

“We found only the cushions, and a few planks” floating in the water, he told the newspaper. There was no sign of the ship, and he immediately called the coast guard.

The boat, identified by Italian officials as the Bayesian, is an Italian-made 56-meter-long sailing yacht first launched in 2008, according to the website marinetraffic.com, which tracks ships. It sails under the flag of Britain, and was built by Perini Navi, an Italian luxury yacht maker.

Eight of the 15 passengers who were rescued were taken to hospitals in Palermo, the coast guard said. Camper & Nicholsons, the managers of the yacht, said its priority was to “provide all necessary support to the rescued passengers and crew.”

Giuseppe D’Agostino, the mayor of Santa Flavia, which includes Porticello, said the survivors would be cared for at a local hotel. The city had also brought them immediate necessities, like toiletries and clothes.

He said in a telephone interview that he had not spoken to the survivors since “they’re in shock.”

The youngest passenger onboard, a 1-year-old girl named Sophie, was taken to the Di Cristina hospital in Palermo with her mother, Charlotte, who had some scrapes and cuts, said Domenico Cipolla, director of the pediatric emergency room at the hospital.

Sophie’s father was in the hospital’s adult emergency room and had been in contact with his wife and daughter by phone, Dr. Cipolla said. He was not permitted to release the family’s surname. Both mother and child were in good condition apart from “great emotional stress” he added in a telephone interview.

“We’re comforting them more than curing them,” he said.

Michael J. de la Merced contributed reporting.