Police say there is a full search and rescue operation under way at the site between the campus of Florida International University and student housing.
Several cranes and police dogs are part of the rescue effort.
Police say eight cars are trapped under the rubble and eight people have been taken to the hospital. They said there are “multiple victims,” but declined to say if there are any deaths.
Media reports have ranged between one and 10 deaths. Miami-Dade Police Director Juan Perez chastised reporters for giving out erroneous information and upsetting families. He said only numbers given out at official police news briefings are to be reported.
The bridge was put up to allow students from Florida International University to easily cross a busy and sometimes dangerous eight-lane highway in Sweetwater, a small city east of downtown Miami.
The final 950-ton section that completed the bridge was assembled at a site along the highway and installed in just one day last Saturday to avoid disrupting traffic.
The bridge was set to be open for pedestrians next year.
School officials and the company that built the bridge, Munilla Construction Management, hailed the project as a major achievement.
MCM said on Twitter it is “devastated” and will conduct a full investigation as well as cooperate with other investigators, including the National Transportation Safety Board.
Florida International University is closed for spring break. The timing of the holiday may have prevented an even bigger tragedy.
WATCH: Rescue workers probe debris for victims
WATCH: Aerial view of Florida pedestrian bridge collapse