Police confirmed to Sky News that the victims are two Italians, one Israeli and one Russian.

Attilio Fontana, president of the Lombardy region, described the incident as "very serious".

Italy's fire service said 19 people have been saved, with many reportedly managing to swim to shore.

Sky Italia reported that British passengers were aboard the vessel, which Mr Fontana said had been hired out by tourists.

According to Italian news site La Repubblica, the boat was carrying up to 25 people who were celebrating a birthday when it capsized and sank.

Firefighter video showed pieces of wood floating in the lake as a helicopter flew overhead.

The whirlwind was part of a storm system that hit the northern region of Lombardy on Sunday evening, forcing delays at Malpensa airport.