Rescue workers are combing through the rubble of a pedestrian bridge that collapsed onto several lanes of traffic at Florida International University, but hopes of finding more survivors are fading.
Six people were confirmed dead after the newly built 860-tonne bridge crushed vehicles on one of the busiest roads in south Florida on Thursday.
"Unfortunately, this has turned from a rescue to a recovery operation," a Miami-Dade police spokesman said on Friday morning. The number of the dead could rise as more vehicles could still be under the concrete and twisted metal, he added.
Emergency personnel with sniffer dogs searched for signs of life overnight.
At least 10 people were taken to hospitals and two remained critical, officials and local media reported.
Witnesses told local media the vehicles were stopped at a traffic light when the bridge collapsed on top of them about 1:30pm on Thursday (local time).
At one point, police requested television helicopters leave the area so rescuers could hear for any sounds of people crying for help from beneath the collapsed structure, CBS Miami television said.
Uncertainty about the stability of remaining sections of the bridge hampered rescue efforts, officials said.
"The structure is very fragile, it's very dangerous for rescuers," a police spokesman said at an early morning press conference. "The entire bridge is in jeopardy."
The 53m-long bridge connects the university with the city of Sweetwater and was installed on Saturday in six hours over the eight-lane highway, according to a report posted on the university's website.
"If anybody has done anything wrong, we will hold them accountable," said Florida Governor Rick Scott, at a Thursday night press conference. His office earlier issued statement saying a company contracted to inspect the bridge was not pre-qualified by the state.
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 holiday, which runs from March 12 to March 17.
The US$14.2 million bridge was designed to withstand a Category 5 hurricane, the most dangerous measure by the National Hurricane Center, and built to last 100 years, the university said.
Officials with the National Transportation Safety Board were on the scene early Friday to investigate why it collapsed.