A major highway bridge along the northern Italian coast collapsed during a torrential rainstorm, sending concrete and vehicles plunging more than 150 feet and killing at least 22 people with numbers expected to climb.

The collapse in the port city of Genoa created an earthquake-like scene of destruction that left slabs of gray concrete and twisted strands of iron blanketing railroad tracks, buildings and a river bed filled with weeds and marsh grass.

Rescuers scrambled to pull people from the rubble, and searched the devastation using sniffer dogs.

Video shows eye-witnesses screaming just after a section of the bridge gave way. One truck was stopped just a few feet from the edge of the chasm - the edge of the bridge sheared cleanly off.

The death toll in the Genoa bridge collapse has risen to 35, as the race to find any survivors buried in the rubble intensifies. Authorities expect the death toll to increase further.#heartbroken#Genoa #Italy #GenoaBridge #GenoaBridgeCollapse

📷 ⁦@Corriere⁩ pic.twitter.com/rGbfxgfcEY

— DiamondShark (@LadyCaveDiver) August 14, 2018

The Morandi Bridge spans a three-quarter-mile section of the coastal city and carries highway traffic between Italy and France. Traffic was likely heavy as vacationers headed out in advance of a major Italian holiday.

One eye-witness, who gave his name as Andrea Rescigno and said he was in his car at the time of the bridge collapse, said in a phone interview with Genoa TV station Primocanale that he saw "cars and trucks plunging into the void."

"I saw death," Rescigno said. "My wife screamed at me to stop. If not for that we'd be dead now," he told the Washington Post.

The disaster shocked the world but many locals feared the bridge would collapse for years and held their breath every time they crossed the vital arterial road.

Aftermath: A man with his arm in a sling speaks to reporters as he walks away from the scene of the disaster this afternoon. Photo / AP

"Everybody has always done it praying that the bridge wouldn't fall down. Today that happened."

"O Dio, O Dio, O Dio," another onlooker screamed as he recorded massive trusses peeling off the bridge, veiled by a thick sheet of rain.

In the hours after the collapse, footage at the scene showed firefighters and other rescue workers climbing on shattered concrete angled like mountain terrain. Heavy equipment was called in to help move the largest pieces of rubble, and helicopters waited nearby.

Amalia Tedeschi, a firefighter, told RAI state TV dozens of vehicles had been involved in the collapse during a sudden and violent storm in Genoa reported news.com.au.

"It was just after 11:30am [7.30pm AEST] when we saw lightning strike the bridge," eyewitness Pietro M all'Asa was quoted as saying by Italy's Ansa news agency.

"And we saw the bridge going down."

The Morandi Bridge was inaugurated in 1967. It is 90 yards high, just over three-quarters of a mile long, with the longest section between supports measuring 200 yards. Photo / AP

Other images showed a green truck that had stopped on the bridge just short of the edge and the tires of a tractor trailer in the rubble.

One Italian official told ANSA that 30 to 35 cars and three trucks were on the bridge when it collapsed.

The collapse took place just one day before Ferragosto, a major Italian summer holiday, at a point of the year when much of the country is leaving cities and heading to the beach.

"It was just after 11.30 when we saw lightning strike the bridge and we saw it going down," eyewitness Pietro told Italy's Ansa news agency.

One unnamed witness said: 'We heard an incredible roar and first we thought it was thunder very close by.

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

Laurie Merchant, who was in Genoa at the time, told MailOnline: 'The storm this morning was something else: very heavy rain and relentless. There was thunder like never before which sounded like a cannon. I was about five minutes from the bridge and I heard a loud crumbling when it went down.

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. Photo / AP

"All you can hear in the city is the sirens of the emergency vehicles going non-stop from the bridge to the hospital."

"The air ambulance has been hovering most of the day. There are huge numbers of people outside the hospital and on the main shopping street there are two vans for people to donate blood."

Rescuers desperately hunting for survivors are now fearful of explosions from damaged gas lines and some areas have been evacuated while safety checks take place.

World leaders have thrown their support behind the Italian people, ready to provide all necessary assistance.

In an interview with the Italian TV channel TG1, Italy's Transport Minister Danilo Toninelli said Italy would need to perform checkups on highway bridges built between the 1950s and 1970s. He said that "maintenance was not done, and these facts go to show it."

"These kind of tragedies cannot and should not happen in a civil country," Toninelli said.

"Those who will be considered responsible will need to pay to the last cent. It should not be possible to see images like these in a country like Italy."

There were horrifying scenes as rescuers carried bodies from the twisted remains of cars flattened during the collapse. Photo / AP

Italy's new government - a coalition of two populist parties that took power two-and-a-half months ago - had not placed an emphasis on road and highway spending in its platform, but several key figures on Tuesday said that investment is needed.

"The tragic facts of Genoa remind us that the public investments of which we have absolute need are under everyone's eyes," said Claudio Borgi, the head of economic policy for Italy's ruling League party.

"Bridges, roads, aqueducts. Years of potential maintenance postponed and shelved 'because there's no money.' Italians' safety comes first."

In a statement, European Commissioner Jean-Claude Juncker said that he is "deeply saddened" by the collapse.

The bridge had been built in the 1960s and had been restructured two years ago, according to the Reuters news agency, which also said that work was ongoing at the time of the collapse to "shore up the foundation."

Italy, like many developed countries, has issues with aging infrastructure, but it was not clear what caused the bridge to give way.

Italy's transport minister, Danilo Toninelli, said he was heading to Genoa and closely following what seemed "poised to be an enormous tragedy."

Italian Prime Minister Giuseppe Conte was planning to head to Genoa today as well.

Dramatic pictures show the scale of the collapse, with vast mounds of concrete and steel lying twisted in the valley. Photo / AP