Rome — Six people, including two U.S. nationals, were believed to be missing Monday after a sailboat sank off the coast of the southern Italian island of Sicily during a violent storm. The 184-foot Bayesian had been anchored about half a mile off the port of Porticello, near Palermo, with 22 people on board — 10 crew members and 12 passengers. 

The vessel sank at about 5 a.m. local time (11 p.m. Eastern, Sunday) after being hit by a possible waterspout spawned by the storm. Italian media said the winds snapped the boat’s mast, unbalancing the vessel causing it to capsize.

Fifteen of those on board were able to get out of the boat and were rescued by a Dutch-flagged vessel that was anchored in the immediate vicinity. They were brought ashore by Italian Coast Guard and firefighters.

One body — an unidentified male — was recovered, but six people remained missing, the Coast Guards said, including Americans, British and Canadian nationals. Italian media said there were two U.S. nationals among those missing, but CBS News was unable to immediately reach the Coast Guard to confirm that number.

Among the survivors was a 1-year-old British girl who was being treated at a nearby hospital along with her parents. They were doing well, according to Italian media.

A search effort was still underway later Monday in the area, with four Coast Guard vessels, a Coast Guard helicopter and a dive team from the national Fire Brigade taking part. The Bayesian appeareed to have sunk in an area with a depth of about 160 feet.

According to Italian media, Fire Brigade divers had reached the boat and seen bodies trapped inside some of the cabins.

Witnesses said the boat appeared top have sunk quickly. 

“I was at home when the tornado hit,” fisherman Pietro Asciutto told a local news outlet. “I immediately closed all the windows. Then I saw the boat, it had only one mast, it was very large. I suddenly saw it sink… The boat was still floating, then suddenly it disappeared. I saw it sink with my own eyes.”

Dozens of migrants have died attempting to reach Sicily and smaller Italian islands in the region over recent years. Sicily sits only about 100 miles from the east coast of Tunisia in north Africa, and the Mediterranean crossing has been a frequent site of both nautical rescues and disasters as smugglers routinely send small boats overloaded with desperate people into the sea.