At least 4 dead in collapse

A pedestrian bridge that was under construction collapsed onto a busy Miami highway Thursday afternoon, crushing vehicles beneath massive slabs of concrete and steel and killing at least four people, authorities said.

Search-and-rescue crews worked into the night, using dogs, search cameras and sensitive listening devices in a frantic search to find survivors among the debris.

"Everybody is working hard to make sure we rescue anyone who can be rescued," Florida Gov. Rick Scott said.

But Miami-Dade police director Juan Perez said hopes were dwindling as the hours passed.

"We know that there's going to be a negative outcome at the end of the day," Perez said.

Four people were found dead amid the chaotic scene, and nine victims were taken "early on" to hospitals, Fire Chief Dave Downey said without elaborating on their conditions.

The partially built 950-ton (860-metric ton) bridge had been assembled by the side of the highway and moved into place Saturday to great fanfare. The span stretched almost 200 feet (60 metres) to connect Florida International University with the city of Sweetwater. It was expected to open to foot traffic next year.

Scott said an exhaustive investigation will uncover "why this happened and what happened," and he vowed to hold accountable those responsible.

National Transportation Safety Board chairman Robert Sumwalt III said a team of specialists was heading to Miami on Thursday night to investigate.

Renderings of the finished bridge showed a tall, off-centre tower with cables attached to the walkway to support it. When the bridge collapsed, the main tower had not yet been installed, and it was unclear what the builders were using as temporary supports.

Kendall Regional Medical Center received 10 injured people. Of those, two were in "extremely critical" condition and eight were stable with injuries such as broken bones, bruises and abrasions, said Dr. Mark McKenney, the hospital's director of general surgery.

Of the two more serious cases, one arrived in cardiac arrest but was revived. The other had a serious brain injury, McKenney said.

The main companies behind the $14.2 million construction project have faced questions about their past work, and one was fined in 2012 when a 90-ton (80-metric ton) section of a bridge collapsed in Virginia.

Munilla Construction Management, or MCM, the Miami-based construction management firm that won the bridge contract, had a news release on its website touting the project with FIGG Bridge Engineers, a Tallahassee firm. After the collapse, it said the site had become temporarily unavailable due to increased web traffic. "It has since been restored."

MCM said on Twitter that it is "a family business and we are all devastated and doing everything we can to assist. We will conduct a full investigation to determine exactly what went wrong and will co-operate with investigators on scene in every way."

FIGG said in a statement, "In our 40-year history, nothing like this has ever happened before."

But FIGG was fined in 2012 after a 90-ton (80-metric ton) section of a bridge it was building in Virginia crashed onto railroad tracks below, causing minor injuries to several workers. The citation from the Virginia Department of Labor and Industry said FIGG did not properly inspect a girder and had not obtained written consent from its manufacturer before modifying it, according to a story in The Virginian-Pilot.

Court documents show that MCM was accused of substandard work in a lawsuit filed earlier this month. The suit said a worker at Fort Lauderdale International Airport, where the company is working on an expansion, was injured when a makeshift MCM-built bridge collapsed under his weight.