A section of a giant motorway bridge collapsed on Tuesday in Genoa, with several people feared dead and dozens injured in what Italy's transport minister said was an “immense tragedy".

Some Italian media, citing sources within the interior ministry, said that at least 11 people had died, though it was not immediately possible to confirm this figure.

Rescuers scouring through the wreckage after part of a viaduct of the A10 freeway in the northern port city collapsed said there were “tens of victims”, while images from the scene showed an entire carriageway plunged on to railway lines below.

Cars and trucks were trapped in the rubble and nearby buildings damaged, according to an AFP photographer at the scene.

Italian media reported that 200 metres of the “Morandi” bridge had fallen away.

The Italian fire service said that the viaduct, located in an industrial area in the west of the city, collapsed at around noon.

“I'm following with the utmost apprehension what is happening in Genoa and what looks like it could be an immense tragedy,” transport and infrastructure minister Danilo Toninelli said on Twitter.

Italy's interior minister Matteo Salvini said he was following events in Genoa “up to the minute” and thanked the emergency services for their swift response.

A fire service spokesperson told AFP that the bridge had mostly fallen on rail tracks 100 metres below and that “cars and trucks” had fallen with the rubble.

“Firefighters are working together and teams of rescuers and police sniffer dogs have been mobilised,” emergency services said on Twitter.

Shares in Italian company Atlantia, which runs much of Italy's motorway network including the collapsed stretch of the A10, plunged on the Milan stock exchange after the news.

They were down 9.7 per cent at 22.48 euros in mid-afternoon, having earlier been temporarily suspended when they drop exceeded 10 per cent.

History of collapses

Genoa is located between the sea and the mountains of northwestern Italy.

Its rugged terrain means that motorways that run through the city and the surrounding area are characterised by long viaducts and tunnels.

The Morandi viaduct, completed in 1967, overspans dozens of railway lines as well as an industrial zone housing several factories.

One factory, immediately next to one of the viaducts support columns, was virtually empty on Tuesday due to a national holiday, and seems to have sustained minimal damage.

French President Emmanuel Macron said on Twitter that France was “by Italy's side in this tragedy and is ready to offer all necessary support”.

Tuesday's incident is the latest in a string of bridge collapses in Italy, a country prone to damage from seismic activity but where infrastructure generally is showing the effects of economic stagnation.

In March last year, a couple were killed when a motorway overpass collapsed on their car near Ancona on the country's Adriatic coast.

A pensioner died in October 2016 when his car was crushed by a collapsing bridge over the SS36 dual carriageway between Milan and Lecco.

That incident was blamed on bureaucratic bungling which led to a fatal delay in the bridge being closed after it was reported to be showing significant cracks.