A pedestrian bridge under construction collapsed Thursday, just days after crews had dropped an elevated 950-ton span in place on a signature project that was intended to give Florida International University students a safe route across the busy roadway.

The massive span — in a sudden, catastrophic failure — crashed down across eight lanes of heavily traveled Tamiami Trail, flattening eight cars. The death toll remained uncertain as rescue crews continued to work into the night to reach vehicles but late Thursday Miami-Dade fire chief Dave Downey confirmed at least four people had been killed, including a student from FIU, police sources said.