A Port Authority bus that was on a bridge when it collapsed, Jan 28, 2022, is visible in Pittsburgh's East End.  (GENE J. PUSKAR/AP)

WASHINGTON – US President Joe Biden stopped to look at a Pittsburgh bridge that collapsed just hours before he arrived for a scheduled visit to the city on Friday, dramatically underscoring the urgency of his drive to rebuild the United States' creaky infrastructure.

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Ten people suffered minor injuries in the collapse of the half-century-old Fern Hollow Bridge, including four who were taken to the hospital, city officials said.

In this aerial image taken with a drone, vehicles rest on a bridge following its collapse on Jan 28, 2022, in Pittsburgh. (GENE J. PUSKAR/AP)

One emergency worker described the scene after the collapse as loud as a jet engine. Biden praised the work of rescuers, noting a natural gas leak that was not stopped until some 30 minutes after first responders arrived at the scene.

More than 220,000 US bridges need major repair work or should be replaced, according to an analysis by the American Road and Transportation Builders Association analysis in 2021. That figure represents 36% of all US bridges

"The idea that we have been so far behind on infrastructure, for so many years – it's just mind-boggling," the president said during the inspection.

Rescuers rappelled at least 150 feet into Fern Hollow, and used ropes to pull people to safety after the snow-covered span over the ravine collapsed around 6 am (1100 GMT), Pittsburgh Fire Chief Darryl Jones said.

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Four vehicles were on the bridge when it fell and the cause of the collapse is under investigation, Jones added.

Ed Gainey, mayor of Pittsburgh, revealed that the bridge over Hot Dog Dam Dog Park was last inspected in September.

Vehicles that were on a bridge when it collapsed are visible as US President Joe Biden visits the site where the Fern Hollow Bridge collapsed, Jan 28, 2022, in Pittsburgh's East End. (ANDREW HARNIK/AP)

Residents and motorists have been urged to avoid the area.

More than 220,000 US bridges need major repair work or should be replaced, according to an analysis by the American Road and Transportation Builders Association analysis in 2021. That figure represents 36 percent, or more than one-third, of all US bridges.

The states with the most serious or worse bridge conditions are Iowa, Oklahoma, Illinois, Pennsylvania, Missouri, and Louisiana, the study also showed.

Emergency vehicles are parked at the edge of a bridge that collapsed, Jan 28, 2022 in Pittsburgh's East End. (GENE J. PUSKAR/AP)

In a statement on Friday, Lieutenant Governor of Pennsylvania John Fetterman called the collapse "the latest in a long line of preventable, man-made disasters."

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"Our infrastructure is failing our people. Our roads and bridges, which are supposed to connect us and bring us together, are increasingly putting us in danger," Fetterman said.