MIAMI, United States (AFP) — Investigators were combing the scene of a footbridge collapse in Miami on Friday to determine how a brand new structure could fail in less than a week, as police said the death toll of six was set to rise.

The operation has shifted from rescue to body recovery, with engineers fearing the support structures at either end of the bridge could also come down, Alvaro Zabaleta, police spokesman for Miami-Dade county, told reporters.

“The entire bridge is in jeopardy,” he said.

Juan Perez, director of the Miami-Dade police department later told reporters that a team of government prosecutors were on the scene as part of the investigation, but stressed it was too soon to say whether criminal charges would be brought.

“It is important that we understand, this is a homicide investigation. That’s all it is,” he said. “That means that somebody died… It does not mean there (are) criminal charges looming or pending or anything like that.”

The toll meanwhile was likely to go up when authorities extracted and identified the remains of victims in vehicles trapped under the rubble, he added.

The walkway, which connects Florida International University to a student housing area, went up less than a week ago but was not yet operational.

Ten people were taken to hospital, Zabaleta said, with emergency crews working all through the night at the scene.

Video footage showed the concrete structure suddenly crashing onto the road below.

At least eight cars were trapped when the 950-ton (tonne) bridge suddenly gave way on Thursday, Miami-Dade Fire Rescue Division Chief Paul Estopinan said earlier.

Police detective Juan Carlos Llera said when the bridge came down, it “sounded like an explosion. A huge bang.”

“It looks like a disaster area. It looks literally like a bomb went off,” Llera told AFP.

Miami Fire Chief Dave Downey meanwhile emphasized there was no hope of finding survivors. “We exhausted last night all of our search and rescue capabilities in the hopes of finding additional survivors,” he said. “This is going to be a long term operation.”

The bridge was suspended from cables which had come loose and while they were being tightened, the whole thing collapsed, Florida Senator Marco Rubio wrote on Twitter.

The bridge had only been installed on Saturday, ahead of its planned opening in 2019. One shaken driver, Lynnell Collins, told CNN he was about to make a right turn when “the whole thing really just came down.”

“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.

The university had only recently been celebrating the construction of the bridge across a busy and dangerous section of highway that students said had been the scene of accidents.

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.

Munilla Construction Management, which was also involved, also issued a statement of condolence. Bridge collapses in the United States are infrequent despite rising risks associated with aging infrastructure.

The deadliest such incident this century was in Minneapolis, Minnesota in 2007, when an eight-lane bridge collapsed into the Mississippi River, killing 13 people.