Italy's interior minister Matteo Salvini said on Tuesday "around 30" have been killed after a motorway bridge collapsed in the northwestern port city of Genoa.
"Unfortunately there are around 30 dead and many injured in a serious condition," Salvini told reporters in the Sicilian city of Catania.
The collapse, which saw a vast stretch of the A10 freeway tumble on to railway lines in the northern port city, was the deadliest bridge failure in Italy for years, and the country's deputy transport minister warned the death toll could climb further.
Rescuers scouring through the wreckage, strewn among shrubland and train tracks, said there were "tens of victims", while images from the scene showed an entire carriageway plunged to the ground.
Cars and trucks were trapped in the rubble and nearby buildings damaged by vast chunks of concrete, according to an AFP photographer at the scene.
(Rescuers work among the rubble of the collapsed Morandi highway bridge in Genoa, northern Italy, on Tuesday. AP photo)
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 (1000 GMT).
"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 far-right 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 their drop exceeded 10 per cent.
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 viaduct's support columns, was virtually empty today 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.