As the president was helped up by an Air Force officer and two members of his US Secret Service detail, he was seen pointing behind him at a sandbag.

Joe Biden has tripped and fallen during a graduation ceremony at the US Air Force academy.

The American president, 80, was quickly helped up by three people, and walked back to his seat unassisted following the incident in Colorado.

As the leader was helped up, he pointed behind him, seeming to indicate what he tripped over.

White House communications director Ben LaBolt said Mr Biden was fine.

"There was a sandbag on stage while he was shaking hands," he said on Twitter.

Mr Biden, who stood for much of the hours-long ceremony to shake hands with graduates, appeared to trip over something and fell to his knees towards the end as he handed out the last diploma.

He was helped up by an Air Force officer as well as two members of his US Secret Service detail. Onlookers, including some members of the official delegation on stage, looked over in concern before the leader returned to his seat.

At the presentation, he gave salutes to the blue-uniformed graduates.

In his address in Colorado Springs to more than 900 cadets, the US commander-in-chief warned graduates they will enter service in an increasingly unstable world, citing challenges from Russia and China.

The Democrat president is running for re-election in 2024.

Speaking on the campaign trail in Iowa, the frontrunner for the Republican nomination next year, Donald Trump, said the fall was "not inspiring", adding the "whole thing is crazy".

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