Aerial footage showed more than 200 metres (650 feet) of the viaduct, known locally as the Morandi bridge, completely destroyed.
Motorist Alessandro Megna told RAI state radio he had been in a traffic jam below the bridge and seen the collapse.
But he added that they were about to launch a 20 million euro ($22.7 million) bidding process for significant safety work on the bridge. "It seemed like a scene from a film, it was the apocalypse", he added.
Italy's department for civil protection said 35 cars and three heavy vehicles were under the bridge and a transport official said eight people were seriously injured. The death toll is likely to rise as multiple people remain missing.
A 2011 report by Italian highways company Autostrade per l'Italia said that the bridge had been suffering from degradation.
"I was driving along the bridge, and at a certain point I saw the road in front of me collapse, and I went down with the auto", Capello, who is now a firefighter, told TV news channel Sky TG24. It called for a "Marshall Plan" to fix or replace tens of thousands of Italian bridges and viaducts built in the 1950s and 1960s.
"These kind of tragedies can not and should not happen in a civil country", Italy's transport minister, Danilo Toninelli, told the Italian TV channel TG1.
Autostrade per l'Italia said on Wednesday that it had carried out regular, sophisticated checks on the structure before the disaster and that these had provided reassuring results.
Smash Bros. Ultimate: 5 New Characters Revealed!
Classic mode , which made its debut way back in the very first Super Smash Bros game for N64, will be returning in Ultimate . Music was previously tied to each stage , but now the selections are only tied to the franchise represented by the stage .
Stefano Marigliani, the Autostrade official responsible for the Genoa area, told Reuters: "The collapse was unexpected and unpredictable".
However, locals say that the bridge has had problems for years, and that it was often attended to by repair crews, but the fixes were never long-lasting, and many in Genoa had petitioned the authorities to replace it.
Rescuers scoured the wreckage of Italy's bridge collapse on Wednesday (Aug 15) as the death toll climbed to 38 and the government blamed the bridge's private owner, demanding resignations and moving to strip its toll concession.
The design of the bridge has been criticized in the past.
The collapse in Genoa occurred during a torrential rainstorm and left slabs of gray concrete and twisted strands of iron blanketing railroad tracks, buildings and a river bed filled with weeds and marsh grass.
Restructuring work was carried out in 2016 on the 1.2 km-long bridge, first completed in 1967.
The disaster, on a major interchange connecting Genoa and other northern cities with beaches in eastern Liguria into France, focused attention on Italy's aging infrastructure, particularly its concrete bridges and viaducts built in the postwar boom of the 1950s and 1960s. "The risk of collapses is underestimated, the works built at that time are coming to an age when they are at risk".
The government has already pledged to increase public investment and lobby the European Commission to have the extra spending excluded from EU deficit calculations. Defence Minister Elisabetta Trenta said the army was ready to offer manpower and vehicles to help with the rescue operations.