Rescuers from all over northern Italy came to help. Photo: EPA

Injured people were winched to safety. Photo: BBC News

The interior minister said at least 35 people were killed when dozens of vehicles fell 45m (148ft).

About 16 people were injured in the collapse and the number missing ranges from four to 12.

About 250 firefighters from across Italy are taking part in the search, using sniffer dogs and climbing gear.

"We're not giving up hope," fire official Emanuele Giffi told AFP news agency, vowing teams would work "round the clock until the last victim is secured".

More than 400 people have been evacuated amid fears other parts of the bridge might fall.

The cause of the disaster, which occurred during torrential rain, was not immediately clear but questions had been raised about the safety of the structure.

Interior Minister Matteo Salvini has vowed to bring anyone responsible for the collapse to book.

The Morandi Bridge, built in the 1960s, stands on the A10 toll motorway, an important conduit for goods traffic from local ports, which also serves the Italian Riviera and southern coast of France.

What are the challenges facing rescuers?

The BBC's James Reynolds at the scene says firefighters have been working their way into small cracks in an effort to find anyone who might still be trapped in a vehicle.

Genoa police spokesperson Alessandra Bucci told Reuters it was thought that people were still alive.

Mr Salvini said three children, aged eight, 12 and 13 were among the dead.

The Italian fire service tweeted a video of one person being extracted and carefully lowered on cables from a shattered vehicle, which was suspended in the wreckage of the bridge, high above the ground.

Between 30 and 35 cars and three heavy vehicles were on the bridge at the time of the collapse.

A huge tower and sections of the bridge collapsed on to railway lines, a river and a warehouse.

The car of Davide Capello, 33, a former goalkeeper for Serie A side Cagliari, came down in the collapse but he survived.

"I was able to get out... I don't know how my car wasn't crushed. It seemed like a scene from a film, it was the apocalypse," he said.

Marcello de Angelis, who is co-ordinating the Italian Red Cross rescue effort, told the BBC that rescuers were treating the disaster like an earthquake.

"There might be the possibility of some niches being created by the rubble itself, with people being protected by the rubble," he said.

"The units that we have sent we use during earthquakes. So it is the same sort of situation - and also the risk of other collapses, obviously, is the same."

How did the bridge collapse?

A section measuring about 200 metres fell at around 11:30 local time (09:30 GMT). Police say there was a violent cloudburst at the time.

An unnamed witness quoted by Italy's Ansa news agency said: "We heard an incredible roar and first we thought it was thunder very close by.

"We live about 5km [three miles] from the bridge but we heard a crazy bang... We were very scared... Traffic went completely haywire and the city was paralysed."

The collapse of the bridge was an "incident of vast proportions on a vital arterial road, not just for Genoa, but for the whole country", said the governor of Liguria region, Giovanni Toti.

An unnamed witness quoted by Italy's Ansa news agency said: "We heard an incredible roar and first we thought it was thunder very close by.