Ten people were injured after a bridge collapsed in Pittsburgh, U.S. state of Pennsylvania, on Friday morning, said officials.

The injuries are all minor and not life-threatening. Three people were transported to the hospital, Pittsburgh's fire chief Darryl Jones told reporters.

Four vehicles were on the bridge when it fell and the cause of the collapse is under investigation, Jones added.

U.S. President Joe Biden later visited the site where he vowed more U.S. investment.

"The idea that we have been so far behind on infrastructure, for so many years - it's just mind-boggling," the president said.

(With input from agencies)