A two-lane bridge in Pittsburgh collapsed on Friday, hours ahead of a visit by President Joe Biden to the Pennsylvania city, dramatically underscoring the urgency behind his drive to rebuild the United States' creaky infrastructure.
Biden told reporters after landing near Pittsburgh early in the afternoon that he planned to go the site of the collapse.
After the snow-covered span collapsed into a ravine around 6am local time (midnight NZT), rescue workers rappelled at least 46 metres into the gully, and used ropes to help pull people to safety, Pittsburgh Fire Chief Darryl Jones said.
"They helped the fire-fighters that were here initially on scene, also did like a daisy chain, with hands just grabbing people and pulling them up," Jones said.
Ten people suffered minor injuries, including four who were taken to the hospital, city officials said. Jones added that crews planned to search under the Forbes Avenue bridge for any victims.
The collapse also caused a massive natural gas leak that forced the evacuation of several families from their homes before being brought under control, Jones said.
The US National Transportation Safety Board said it was sending a team to the site.
The incident was a high-profile example of the need to rebuild the nation's ageing bridges, highways and other infrastructure with money from a US$1 trillion (NZ$1.53 trillion) spending bill that was a signature achievement of Biden's first year in office.
Images of the collapse showed the span buckled into three large sections, with several vehicles piled in the rubble of the collapsed roadway at the bottom of the ravine. The tail end of a long, red city bus appeared trapped by the rubble.
Pennsylvania has 3,198 bridges rated as being in poor condition, according to the US Department of Transportation.
The collapse came just two weeks after Pennsylvania got US$327 million (NZ$500m) from the US Department of Transportation for bridge repair as part of the Biden administration's new infrastructure law. Pennsylvania's share of the bridge-repair money is the third largest state allocation, behind only California and New York.
Biden, whose approval ratings have fallen in recent months amid a surge in the Covid-19 pandemic and inflation, got a boost on Thursday when the Commerce Department reported the US economy grew the fastest in nearly four decades in 2021.
In Pittsburgh, the president will tour Mill 19, a former steel mill building now serving as a research and development hub, before hailing the US economy's strong recovery from the pandemic, the White House said.
"The president will talk about the remarkable economic progress we've made over his first year in office - including the fastest single year of job growth in American history, the biggest unemployment drop on record and, as we learned on Thursday, the fastest economic growth in 2021 in almost four decades," a White House official said.
The Democratic president was returning to the site of his first campaign event in 2019. He is expected to tout the creation of 367,000 manufacturing jobs since he took office a year ago, and highlight the $1 trillion infrastructure bill - which was a rare bipartisan victory in a deeply divided Congress.
The president also plans to talk about his push to rebuild American competitiveness and beat China in a race to dominate the global economy, the official said.
In recent days, General Motors Co has said it would invest $7 billion (NZ$10.7bn) in Michigan to expand electric vehicle production and Intel Corp has said it would invest $100 billion (NZ$153bn) to build a chip-making complex in Ohio.
Mill 19 is home to Carnegie Mellon University's Manufacturing Futures Institute, and hosts a robotics laboratory and a technology training site.