Miami police have said there are several fatalities after a newly installed pedestrian bridge collapsed at Florida International University.
Images of the buckled structure at the college in Miami were shared across social media on Thursday afternoon.
The 950-ton bridge was erected on Saturday, CBS Miami reports.
An unknown number of people in eight cars were still trapped beneath the bridge, which was built over a motorway, Miami officials said.
At least eight people have been taken to hospital to be treated for injuries, officials said at a news conference on Thursday.
Florida Highway Patrol Lt Alejandro Camacho earlier told the BBC that the number of fatalities was unclear. He earlier told CBS News there were several fatalities.
US Senator Bill Nelson told local media six to 10 people were killed in the collapse, but the exact figures have yet to be confirmed by law enforcement.
Aerial footage shows first responders trying to get under the bridge to trapped cars.
The university issued a statement saying rescue efforts were still underway.
“We are shocked and saddened about the tragic events unfolding at the FIU-Sweetwater pedestrian bridge,” said a university spokesperson.
“At this time we are still involved in rescue efforts and gathering information.”
Miami-Dade County Emergency Management urged commuters to avoid the area.
A witness told ABC News that the screams coming from the cars were “terrifying”.
“As soon as I looked outside, I saw dust flying everywhere,” Tiona Page said. “I knew the bridge had collapsed.”
Another witness, Damany Reed, told CBS News: “I heard a big kaboom…it sounded continuous. We look outside…we thought something had fallen but it was the bridge that collapsed. It was just surreal at that moment and pretty scary”.
Florida Governor Rick Scott responded to the accident on Twitter: “I have spoken with Miami-Dade County Police Chief Juan Perez about the pedestrian bridge collapse at FIU.
“I will be in constant communication with law enforcement throughout the day.”
White House spokeswoman Sarah Sanders said President Donald Trump was aware of the incident and would send any assistance needed to help local law enforcement officials.
The bridge, which connected the college to a student housing area, had long been requested by students and staff at the university so they could avoid the traffic below, according to the Miami Herald.
In August 2017, a student was hit and killed by cars while crossing the busy road.
Munilla Construction company (MCM), a family-owned contractor that helped build the bridge, tweeted “thoughts and prayers” for those affected by the tragedy.
“We will conduct a full investigation to determine exactly what went wrong and will cooperate with investigators on scene in every way,” the firm tweeted.
The university had touted the new swinging span on Twitter just days ago.
The 174ft (53m) cable-supported footbridge was to be publicly opened in 2019, local media say.
Costing $14.2m (£12.5m), it was funded by the US Department of Transportation.
NBA basketball team Miami Heat tweeted their support to the FIU community.
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