Engineer warned of cracking in Florida bridge before collapse

The chief engineer of a Florida bridge project warned authorities of cracking in the structure days before it collapsed, killing at least six people, said the US state's department of transportation.

At least six people were killed when the pedestrian bridge at Florida International University collapsed. Source: AAP

Denney Pate left a voicemail on a Florida Department of Transportation employee's landline on March 13, two days before it came crashing down on the major road beneath, the department said in a statement.

The voicemail - which was not heard until Friday because the employee it was left for was out of the office - mentioned a problem, but did not warn that structural failure was imminent.

Authorities say the pedestrian bridge that failed had been put to a "stress test" and its cables were being tightened when it collapsed. Source: AAP

There was "some cracking that's been observed on the north end of the span," Pate said, according to a transcript of the call.

"Obviously some repairs or whatever will have to be done but from a safety perspective we don't see that there's any issue there," Pate said.

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

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

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