A newly installed pedestrian bridge over a major road in Miami collapsed on Thursday (Mar 15), killing four people and trapping multiple cars below.
The walkway, which connected Florida International University to a student housing area, went up less than a week before.
"We have located up to four victims. Four deceased," Miami-Dade fire chief Dave Downey told a news conference.
Emergency personnel with sniffer dogs searched for signs of life amid the wreckage of concrete, twisted metal and that rained from the collapsed structure and crushed vehicles on one of the busiest roads in South Florida.
Maurice Kemp, the area's deputy mayor, said the search for survivors had not yet been abandoned.
"Miami-Dade county and our partner agencies ... have been working feverishly in the search and rescue mode to ascertain how many victims there are and rescue as many as we can," Kemp told journalists.
"We will continue in this mode until we are certain there are no more viable victims, and at some point, we will transition into an investigation and recovery mode, but we're not there yet," he said.
Miami-Dade Fire Rescue Division Chief Paul Estopinan had earlier said that at least eight cars were trapped when the 950-tonne concrete bridge suddenly gave way.
The bridge had only installed on Saturday, ahead of its planned opening in 2019.
The bridge was intended to provide a walkway over the busy street where an 18-year-old female FIU student from San Diego was killed while trying to cross 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.
"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.
Isabella Carrasco, who said she arrived on the scene just after the collapse, told reporters that some cars were "completely crushed", and there was "just a lot of debris everywhere".
She said she saw one woman get out of a car that was "just nicked" and rescue personnel performing life-saving CPR on another person in the street.
Another shaken driver, Lynnell Collins, told reporters he was about to make a right turn when "the whole thing really just came down".
"WHOLE THING BROKE"
"After the whole thing broke, I was freaking out. I got out of my car and me and a few other people were sprinting over there. We started helping people whose cars were at least half crushed and whoever was easily saved."
He said he saw two trucks that were "completely crushed".
"We are shocked and saddened about the tragic events unfolding at the FIU-Sweetwater pedestrian bridge," Florida International University said in a statement.
"At this time we are still involved in rescue efforts and gathering information."
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.
It had been erected using an accelerated modular building method that enabled it to go up in the space of a day.
"We are stunned by today's tragic collapse of a pedestrian bridge," said FIGG Engineering Group, one of the partners involved in the walkway's construction.
"We will fully cooperate with every appropriate authority in reviewing what happened and why," the firm said in a statement.
"In our 40-year history, nothing like this has ever happened before."
"Continuing to monitor the heartbreaking bridge collapse at FIU - so tragic," President Donald Trump wrote on Twitter.
"Many brave First Responders rushed in to save lives. Thank you for your courage. Praying this evening for all who are affected," he said.
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.
Bridge collapses in the United States are infrequent despite rising risks associated with ageing infrastructure.
The deadliest this century was the 2007 collapse of an eight-lane bridge in Minneapolis, Minnesota, which killed 13 people.