Between six to 10 people have been killed in the collapse of a pedestrian bridge on to a busy motorway in Florida - and search and rescue teams are scouring the rubble for more casualties.

Eight vehicles were trapped in the wreckage of the 950-ton bridge at Florida International University and eight people have been taken to hospitals, officials told a news conference.

Emergency personnel with sniffer dogs searched for signs of life amid the wreckage of concrete and twisted metal that crushed vehicles on one of the busiest roads in South Florida.

At one point, police asked television helicopters to leave the area so rescuers could hear for any sounds of people crying for help from beneath the collapsed structure, the Miami TV station said.

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"We heard a loud bang behind us and we looked back and the bridge had completely collapsed," Isabella Carrasco, a student at the University of Miami, told CNN.

"We thought something fell," Damany Reed, who witnessed the collapse, told CBS Miami.

"But then we saw the bridge collapse and it was just surreal. It was very scary."

Emergency personnel responds to a collapsed pedestrian bridge connecting Florida International University. Photo / AP
Emergency personnel responds to a collapsed pedestrian bridge connecting Florida International University. Photo / AP

Ricardo Dejo, a Florida International University civil engineering student, told CNN he saw cars pinned beneath the bridge. "I can't describe it," Dejo said. "We were really excited about the bridge. Everything looked fine. I went underneath it with my own car and it looked great."

Dramatic images of the buckled structure were shared across social media this morning (NZT).

Television footage showed several people loaded onto ambulances immediately after the collapse.

The bridge only went up on Saturday, CBS Miami reported.

"We are shocked and saddened about the tragic events unfolding at the FIU-Sweetwater pedestrian bridge," the university said. "At this time we are still involved in rescue efforts and gathering information."

The Miami Herald reported an unknown number of people were trapped under the bridge.

It is unclear how many people have been injured on or beneath the bridge.

Florida Governor Rick Scott tweeted that he had spoken to Miami-Dade County Police Chief Juan Perez about the bridge collapse and would be in constant communication with law enforcement throughout the day.

Miami-Dade Fire Rescue Department said it was securing the structure while searching for injured people.

The Miami Herald said that the bridge has long been requested by people at the university so they could avoid the perilous road.

In August last year, a student was killed by cars while crossing.

"Our family's thoughts and prayers go out to everyone affected by this terrible tragedy," said MCM, one of the companies that contributed to the construction of the bridge.

"The new University City Bridge, which was under construction, experienced a catastrophic collapse causing injuries and loss of life."

The Miami-based construction management firm took its website down after the collapse.

But an archived version of the website featured a news release touting the project.

"This our first Design-Build with FIGG Bridge Engineers, a nationally acclaimed, award-winning firm based out of Tallahassee.

"FIGG has designed iconic bridges all over the country, including Boston's famous Leonard P. Zakim Bridge and Florida's Sunshine Skyway Bridge."