Police investigating the collapse of a pedestrian bridge in Miami have said they expect to find more bodies in the rubble, as investigators work to determine why the new structure failed.
Six deaths have already been confirmed and Miami-Dade Police director Juan Perez told reporters he expects additional victims to be found as the massive concrete structure is removed.
Mr Perez said the main priority is getting to the victims in crushed vehicles under the rubble as quickly as possible.
Authorities said one victim is confirmed to have been a student at nearby Florida International University. No identities of those killed have been released.
Authorities said the cables suspending a pedestrian bridge were being tightened after a "stress test" when the 950-ton concrete span collapsed on to a busy highway on Thursday afternoon, days after its installation was celebrated as a technological innovation.
As state and federal investigators worked to determine how and why the five-day-old span failed, Florida politicians pointed to the stress test and loosened cables as possible factors, but Mr Perez asked people not to jump to conclusions.
"This is a tragedy that we don't want to reoccur anywhere in the United States," he said. "We just want to find out what caused this collapse to occur and people to die."
Senator Marco Rubio tweeted that cables suspending the span had loosened, and the engineering firm ordered that they be tightened. "They were being tightened when it collapsed," he said.
Experts from the National Transportation Safety Board and the Occupational Safety and Health Administration joined police in taking over command of the scene.
First responders had spent hours racing to find survivors in the rubble of the 175ft span using hi-tech listening devices, trained sniffing dogs and search cameras.
The 14.2 million dollar pedestrian bridge was supposed to open in 2019 as a safe way to cross six lanes of traffic between the Florida International University campus and the community of Sweetwater, where many students live.
Florida governor Rick Scott said investigators will get to the bottom of "why this happened and what happened", and if anyone did anything wrong, "we will hold them accountable".
Mr Rubio, who is an adjunct professor at the school, noted the pedestrian bridge was intended to be an innovative and "one-of-a-kind engineering design".
When finished, the bridge would have been supported from above, with a tall, off-centre tower and cables attached to the walkway.
That tower had not yet been installed, and it was unclear what builders were using as temporary supports.
An accelerated construction method was supposed to reduce risks to workers and pedestrians and minimise traffic disruption, the university said.
The school has long been interested in this kind of bridge design; in 2010, it opened an Accelerated Bridge Construction Centre to "provide the transportation industry with the tools needed to effectively and economically utilise the principles of ABC to enhance mobility and safety, and produce safe, environmentally friendly, long-lasting bridges".
The project was a collaboration between MCM Construction, a Miami-based contractor, and Figg Bridge Design, based in Tallahassee. Figg is responsible for the Sunshine Skyway Bridge across Tampa Bay.
Both companies have been involved in bridge collapses before.
Figg was fined in 2012 after a section of a bridge it was building in Virginia crashed on to railway tracks and injured several workers, according to a story in the Virginian-Pilot.
MCM was accused of substandard work in a lawsuit filed this month by a worker injured when a makeshift bridge MCM built at Fort Lauderdale International Airport collapsed under his weight.
VIDEO: Florida International University bridge collapses. View from student dorms. pic.twitter.com/4wuD89IPhj— Ana Demendoza (@AnaDemendoza_) March 15, 2018
Another dispute resulted in a 143,000 dollar judgment against MCM over an "arguable collapse" at a Miami-Dade bridge project.
A review of OSHA records showed MCM has been fined for 11 safety violations in the past five years totalling more than 50,000 dollars after complaints involving its Florida worksites.
Both companies expressed condolences for the victims and promised co-operation with investigators.