MIAMI, Florida (REUTERS) - A newly erected pedestrian bridge spanning several lanes of traffic collapsed at Florida International University on Thursday (March 15), killing four people, Miami-Dade County Fire Chief Dave Downey said.

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

At least eight vehicles were trapped in the wreckage of the 950-ton bridge and at least 10 people have been transported to hospitals, officials and doctors told news conferences.

Witnesses told local media the vehicles were stopped at a traffic light when the bridge collapsed, and authorities said there still may be more vehicles trapped underneath.

"We're working our way into the pile trying to create holes that we can actually physically see," Miami-Dade Fire Department Division Chief Paul Estopian told reporters.

The Florida Highway Patrol previously said several people were killed but did not release a figure on fatalities.

At one point, police had requested 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.

Complicating the rescue effort was the uncertainty about the integrity of the bridge, parts of which remained off the ground, much of it inclined, local media reported.

The bridge connects the university with the city of Sweetwater and was installed on Saturday in six hours over the eight-lane highway, according to a story that was posted on the university's website. It was 53m long and weighed 950 tonnes.

"If anybody has done anything wrong, we will hold them accountable," said Florida Governor Rick Scott, at a Thursday night press conference, after his office issued statement saying a company contracted to inspect the bridge was not pre-qualified by the state.

The bridge was intended to provide a walkway over south-west Eighth Street, one of the busiest roads in South Florida. An 18-year-old female FIU student from San Diego was killed while trying to cross the street last August, according to local media reports.

Students at FIU are currently on their spring break vacation, which runs from March 12 to March 17.

Television footage showed firefighters were walking across the flattened wreckage and medics treating injured people. Emergency personnel appeared to be trying to work their way through a hole in the top of the bridge.

'A MIRACLE'

Student Aura Martinez was having lunch in a nearby restaurant with her mother when a waitress told her the bridge had collapsed. She ran outside and helped pull a woman out her car, most of which was flattened by the bridge.

"Her car, it was literally a miracle of God, her car got squished by the bridge from the back, so she was able to get out and she was on the floor and it was just very traumatic," she told the local CBS affiliate.

To keep the inevitable disruption of traffic associated with bridge construction to a minimum, the 53m portion of the bridge was built adjacent to Southwest 8th Street using a method called Accelerated Bridge Construction (ABC). It was driven into its perpendicular position across the road by a rig in only six hours on Saturday, according to a statement released by the university.

President Donald Trump thanked first responders for their courage on Twitter. US Senator Marco Rubio and Florida Governor Rick Scott were at the scene of the collapse.

Munilla Construction Management, which installed the bridge was founded in 1983 and owned by five brothers, according to its website. In addition to its Florida operations, the company also has divisions in Texas and Panama and employs 500 people.

"Munilla Construction Management is a family business and we are all devastated and doing everything we can to assist," the company said in a statement.

FIGG Engineering said it took part in the bridge project and the collapse was a first in its 40-year history.

Both companies said they would cooperate fully with investigators.

Colorado-based engineering company BDI said in a tweet on March 12 that it was "thrilled" to have conducted structural monitoring during the "spectacular" process of moving the bridge into place. The company removed the tweet on Thursday and said in a statement it did so out of respect for individuals affected by the collapse.

Scott's office said FIU picked a firm that was not pre-qualified to check the design of the bridge, which was required because it was such a long pedestrian bridge and other unique characteristics.

"The firm selected, Louis Berger, was not FDOT pre-qualified for this service, which is required under FIU's agreement with the state. FIU's design build team is responsible for selecting a pre-qualified firm and ensuring this process is followed," the governor said in a statement.

Officials at the Miami office of global engineering services firm Louis Berger were not immediately available for comment.