President Joe Biden tripped and fell while handing out diplomas at a graduation ceremony for the US Air Force Academy in Colorado.
Biden, who is the nation’s oldest serving president at 80, was helped back up to his feet and appeared to be unhurt.
The president had been standing for about an hour and a half to shake hands with each of the 921 graduating cadets.
The White House communications director said earlier “he’s fine”.
“There was a sandbag on stage while he was shaking hands,” Ben LaBolt wrote on Twitter after Thursday’s fall.
“I got sandbagged,” the smiling president joked to reporters as he arrived back at the White House that evening.
A White House press pool report earlier said Biden had tripped on a black sandbag while moving on stage.
Footage of the incident shows Biden appearing to point at one of two sandbags used to prop up his teleprompter as he was helped up by an Air Force official and two members of his Secret Service detail.
He was seen walking back to his seat unassisted and later jogging back to his motorcade when the ceremony ended shortly after the accident.
The pool reporter added that the president did not take questions when he returned to his plane.
White House press secretary Karine Jean-Pierre said Biden was feeling “totally fine” and had boarded the plane flashing “a big smile”.
Critics have said Biden is too old to run for a second term as president.
Recent polls suggest a majority of US voters are concerned about his advanced age. He would be 82 at the start of a second term if he wins.
This fall, in addition to previous stumbles from his bicycle and on the way up the Air Force One stairs, could add to those concerns.
Former President Donald Trump, the Republican frontrunner to face Biden in the 2024 White House election, reacted to the incident at a campaign event in Iowa, saying “The whole thing is crazy”.
“I hope he wasn’t hurt,” said Trump, 76, who has often poked fun at Biden’s age. “That’s not inspiring.”
“You got to be careful about that because you don’t – you don’t want that. Even if you have to tiptoe down the ramp,” added Trump, apparently referring to his careful walk of a stage that made headlines in 2020.
He said at the time that the ramp at the US Military Academy in West Point, New York, was slippery, and brushed aside the ensuing media questions about his health as fake news.
Florida Governor Ron DeSantis, another 2024 contender for the Republican nomination, also reacted to the fall during a campaign event in New Hampshire: “We hope and wish Joe Biden a swift recovery from any injuries he may have sustained.
“But we also wish the United States of America a swift recovery from the injuries it has sustained because of Joe Biden and his policies.”
Biden’s last physical examination took place in February.
White House physician Dr Kevin O’Connor wrote at the time: “The President remains fit for duty, and fully executes all of his responsibilities without any exemptions or accommodations.”
Dr. O’Connor added that Biden walks with a “stiffened gait”, largely caused by wear and tear on his spine and nerve damage in his feet, but that his condition was unchanged from a previous physical in November 2021.
Biden is hardly the first commander-in-chief to lose his footing in front of the cameras.
President Barack Obama tripped walking upstairs at a 2012 event, while President Gerald Ford fell down the stairs of Air Force One in 1975.