Four people, including two Italian intelligence personnel and an Israeli, were killed when a tourist boat capsized when strong winds blew in Lake Maggiore in northern Italy.

The 16-metre boat capsized on Sunday evening off Lisanza at the southern end of the lake when a storm suddenly struck.

Firefighters spokesman Luca Carey told AFP the bodies of four people had been found. Among the victims were two members of Italian intelligence.

"On the evening of 28 May, following a maritime accident caused by a violent whirlwind, Claudio Alonsi (62) went missing (...) and Titsiana Barnobi (53 years old). They belong to the intelligence service and were in the area to participate in a party organized for the birthday of one of the participants."

One of the victims is an Israeli "fifteen," according to the Israeli Foreign Ministry. The fourth victim is a Russian citizen, according to the local news site "Varysy News".

Lombardy regional president Attilio Fontana spoke on Sunday evening of a "very serious accident" caused by a "whirlwind".

Italian media reported that about 20 survivors were recovered by other boats or managed to swim ashore. It also noted that the capsized boat was carrying Italian and foreign tourists and sank quickly.

Video footage filmed by firefighters showed a search helicopter flying over rough waters.

Lake Maggiore, located in the south of the Alps, is the second largest lake in Italy and a popular tourist destination.