Gasps from the crowd followed Biden's fall, which came as he handed out the last diploma, forcing the president to come down on his knees.

Biden, who was helped to his feet by Air Force officials, appeared to trip on a black sandbag that was on the stage.

Biden, 80, the oldest president in U.S. history, appeared to be OK and continued to stand as the ceremony concluded a few minutes later.

"He's fine," Ben LaBolt, White House communications director, said in a tweet. "There was a sandbag on stage while he was shaking hands."