About 30 were killed after a motorway bridge collapsed on Tuesday (Aug 14) over the northern Italian port city of Genoa in what the transport minister said was likely to be "an immense tragedy".

A section of a giant motorway bridge in Genoa collapsed on Tuesday (Aug 14) injuring several people. (Photo: AFP)

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

"Around 30 people are dead and many others are seriously injured," Italy's interior minister Matteo Salvini told reporters in Sicily.

An 80-metre section of the bridge, including one set of the supports that tower above it, crashed down in the rain onto the roof of a factory and other buildings, crushing at least one truck and plunging huge slabs of concrete into the river below.

The highway is a major artery to the Italian Riviera and to France's southern coast. Train services around Genoa have been halted.

A picture taken on Aug 14, 2018 in Genoa shows a section of a giant motorway bridge that collapsed earlier injuring several people. (Photo: AFP/Andrea Leoni)

A witness told Sky Italia television he saw "eight or nine" vehicles on the bridge when it collapsed in what he said was an "apocalyptic scene".

Cars and trucks were trapped in the rubble and nearby buildings damaged.

Helicopter footage on social media showed trucks and cars stranded on either side of the 50-metre high collapsed section of the Morandi Bridge. One truck was shown just metres away from the broken end of the bridge.

Some 200 firefighters were on the scene, the fire service said, and Italian news agency ANSA said two survivors had been pulled out of the rubble under the collapse.

The wreckage of a truck is seen after a giant motorway bridge collapsed earlier, on Aug 14, 2018 in Genoa. (Photo: AFP/Andrea Leoni)

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

Police footage showed firemen working to clear debris around a crushed truck, while other fireman nearby scaled broken slabs of the collapsed bridge support.

"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.

Salvini said he was following events in Genoa "up to the minute" and thanked the emergency services for their swift response.

This handout picture provided by the Italian police (Polizia di Stato) on Aug 14, 2018 shows a collapsed section of a viaduct on the A10 motorway in Genoa. (Photo: Handout/Italian Police/AFP)

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 collapsed bridge was built on the A10 toll motorway in the 1960s. Restructuring work on the bridge was carried out in 2016.

The highway operator said work to shore up the foundation of the bridge was being carried out at the time of the collapse, adding that the bridge was constantly monitored.

A view of the collapsed Morandi highway bridge in Genoa, northern Italy on Aug 14, 2018. (Photo: Luca Zennaro/ANSA via AP)

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".

Toninelli told Italian state television the disaster showed the dilapidated state of Italy's infrastructure and a lack of maintenance, adding that "those responsible will have to pay."

"It's not acceptable that such an important bridge ... was not built to avoid this kind of collapse," Italy's deputy transport minister Edoardo Rixi said. "The central section came down."

Rescuers are at work amid the rubble of a section of a giant motorway bridge that collapsed on Aug 14, 2018 in Genoa. (Photo: AFP/Andrea Leoni)

Italy's anti-establishment government which took office in June has pledged to increase public investments and lobby the European Commission to have the extra spending excluded from EU deficit calculations.

"The tragic facts in Genoa remind us of the public investments that we so badly need," said Claudio Borghi, economics spokesman of the right-wing League party, which governs with the 5-Star Movement.

Rescues work among the debris of the collapsed Morandi highway bridge in Genoa on Aug 14, 2018. (Photo: Luca Zennaro/ANSA via AP)

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./.

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