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By Linda Givetash, Lucy Kafanov and Claudio Lavanga

GENOA, Italy — Firefighters continued a round-the-clock search of rubble in this north Italian city Wednesday as questions were raised about what caused a bridge collapse that killed at least 39 people.

Deputy Prime Minister Matteo Salvini warned that whoever was responsible would have to "pay dearly" after an 80-yard section of the Morandi Bridge in Genoa fell following a violent storm Tuesday.

Dozens of cars and three trucks plunged as much as 150 feet to the ground. Around 400 firefighters worked through the night, lifting chunks of concrete to create spaces for rescue teams to check for survivors.

Italian Transport Minister Danilo Toninelli said the government would inspect aging bridges and tunnels across the country to determine if a program of remedial works is required.

Corruption in the public sector has been highlighted as an issue in recent years.

A 2014 report by the European Commission warned that infrastructure projects were at the greatest risk of corruption and infiltration by organized crime as part of Italy's public procurement process.

Such corruption occurs most frequently at the stage when quality checks are carried out, according to experts.

Although Italy has taken steps to curb the issue, a study published last year described corruption in the country's infrastructure as "an elephant in the room" that can send costs soaring up to 50 percent over budget.

"The cost performance of Italian infrastructure is dramatically worse than elsewhere," it said.

Image: Collapsed bridge in Genoa, Italy
Vehicles remained on the Morandi Bridge in Genoa on Wednesday.Luca Zennaro / AP

When the highway overpass was completed in 1967, it was considered innovative for its use of concrete around its cables.

However, traffic levels on it were higher than its designers had envisioned. One expert in such construction, Antonio Brencich at the University of Genoa, had previously called the bridge "a failure of engineering."

"So many people that lived here lost their lives, children. 'Why children, why not me?' This is the thought I have."

David Knight, a structural engineer and an expert in bridge design for the U.K. firm Cake Industries, said corrosion of steel cables within the concrete most likely contributed to the collapse.

Water can seep into concrete and, with exposure to oxygen over many years, cause the steel inside to rust, he said. The blustery storm ranging at the time of the collapse may have added to the pressure.

"That additional wind, that would have normally been resisted ... in this case with the corrosion, pushed it over the edge and caused it to snap," he said.

Regular maintenance, scheduled roughly every 15 years, can prevent this type of failure, Knight said. Modern bridges in Europe are designed to last a century or more.

But the Italian civil engineering society, CNR, said structures dating from when the Morandi Bridge was built had exceeded their lifespan. It called for a "Marshall Plan" to repair or replace tens of thousands of Italian bridges and viaducts built in the 1950s and ’60s. It said that updating or reinforcing the bridges would be more expensive than replacing them with newer designs.

Work to shore up foundations on the Morandi Bridge was being carried out at the time of the collapse, but the highway operator, Autostrade per L'Italia, said it was constantly monitored.

The exact cause is yet to be determined, but Knight said the disaster is a "wake-up call" for governments and bridge owners.

He said it was "very easy" to cut maintenance budgets for infrastructure so that money could be used instead on "high-profile budget items."

Knight added that an investigation would likely reveal failures in several areas, from engineering to financial mangement.

Toninelli, the transport minister, suggested Autostrade would have to contribute to the cost of reconstruction as well as pay heavy fines.

But Autostrade said it had carried out regular, sophisticated checks by "world leaders in testing and inspections" that had provided reassuring results.

Silvia Vieri
Silvia Vieri in Genoa, Italy.Dave Copeland NBC News / Dave Copeland NBC News

Silvia Vieri, who was driving with her boyfriend when the bridge collapsed in front of them, told NBC News that she believes the government is at fault for not investing in the upkeep of infrastructure.

"They spend money on themselves, but not for the community," she said.

Her boyfriend, who is a firefighter, managed to pull three people from the rubble as they waited for help to arrive.

Image: Abandoned vehicles on bridge in Genoa, Italy
Abandoned vehicles remained on the bridge on Wednesday.Valery Hache / Getty Images

"So many people that lived here lost their lives, children," Vieri said. "''Why children, why not me?' This is the thought I have."

The bridge is part of a major route linking the Italian Riviera with France's southern coast.

At least four of the victims were French, according to the country's foreign ministry.

Lucy Kafanov reported from Genoa, Claudio Lavanga from Rome, Linda Givetash from London, and Nancy Ing from Paris.

Nancy Ing, Reuters and Associated Press contributed.