At least 22 people have died after a major four-lane motorway bridge collapsed in Genoa, Italy, during a violent storm.

Italian authorities have said that a 200-metre section of the Morandi Bridge collapsed on Tuesday over an industrial zone.

It is believed 20 vehicles have fallen into the void but authorities are yet to comment on the number of victims.

The disaster occurred on a highway that connects Italy to France on the eve of a major Italian holiday on Wednesday, Ferragosto, and traffic would have been heavier than usual as many Italians traveled to beaches or mountains.

At least one person has been rescued alive from the rubble of the bridge.

Italian news agency ANSA says one person has been rescued alive from the rubble of the bridge collapse near the northern city of Genoa and is being transported by helicopter to a hospital.

There was no immediate word on overall deaths or injuries. Maria Luisa Catalano of the highway police in Genoa said work was ongoing, adding, "we don't know numbers of victims/injured yet."

Interior Minister Matteo Salvini said some 200 fire fighters are responding to the accident.

On Twitter he said: "we are following minute by minute the situation of the bridge collapse in Genoa."

The bridge is an important interchange between the northern regions of Lombardy and Piedmont and the beaches of Liguria, and to the main highway heading westward into France.