MIAMI (AP) — Relatives and friends of people still missing after a pedestrian bridge collapsed on a highway gathered Friday in South Florida, longing and praying for miracles as authorities searched the smashed concrete that has already claimed six lives.

While the families waited, investigators sought to understand why the 950-ton bridge gave way during construction. The cables supporting the span were being tightened following a "stress test" when it collapsed, authorities said.

"This is a tragedy that we don't want to re-occur anywhere in the United States," said Juan Perez, director of the...