As workers slowly break off chunks of a newly built pedestrian brdige that collapsed onto a major road in Miami, a shocking video of the moment at least six people died has come to light.

The footage, captured by the dashboard camera of a car whose driver missed being killed by mere seconds, shows there was no warning the structure was about to give way.

Miami police expect to find an unknown number of bodies in crushed vehicles that remain trapped beneath the rubble.

Their efforts to clear the debris and reach victims are being hampered and slowed by the rubble’s dangerous instability.

The unsettling vision comes as it was revealed that engineers, state and university officials met hours before the bridge collapsed but concluded a crack in the structure was not a safety concern, Florida International University said.

The 950-ton, $US14.2 million bridge plummeted onto traffic on one of the busiest roads in South Florida on Friday (Thursday US time), crushing vehicles stopped at a traffic light on the eight-lane roadway below.

With at least eight vehicles still buried, the death toll is almost certain to rise, said Juan Perez, the Miami-Dade Police Department director.

“We know that there’s people missing, the family members know that there’s people missing, and what we can tell them is that we can assume that they’re in there,” Mr Perez told a news conference.

After searching the site with sniffer dogs, police determined late on Thursday that no one would be pulled out alive.

One of the victims was Alexa Duran, who was studying political science at Florida International University.

Authorities have not released Ms Duran’s name, but her family has said she died.

Three of the victims found on Saturday were identified by police as Rolando Fraga Hernandez, Oswald Gonzalez and Alberto Arias.

Another victim, who died in a hospital after the collapse, was identified by police as Navarro Brown.

Witnesses told local media the doomed motorists had stopped at a traffic light when the bridge came down on top of them around 1.30pm local time.

The meeting on Thursday involved FIGG, which is the private contractor for the overall bridge design, the school, Florida Department of Transportation officials and Munilla Construction Management, which installed the bridge.

A FIGG engineer “concluded there were no safety concerns and the crack did not compromise the structural integrity of the bridge”, the university said in a statement.

About three hours after the meeting concluded, the bridge fell down.

-with AAP