President Joe Biden took a face-first tumble on Thursday after tripping over an obstacle on stage at the Air Force Academy in Colorado, but he appeared unhurt.

Biden, 80, who had delivered the commencement address to graduates of the military academy, had just shaken hands with a cadet and begun walking back to his seat when he fell.

Air Force personnel helped him back up and he did not appear to require further help.

As he rose, Biden pointed to the object that had apparently caught his foot. It resembled a small black sandbag on the stage.

Biden is the oldest person ever in the presidency and is seeking a second term in the 2024 election. His official doctor’s report this year declared him physically fit and he exercises regularly.

In November 2020, shortly after winning his election against the incumbent Donald Trump, Biden broke his foot while playing with a pet dog.(AFP)

•US President Joe Biden falls during the graduation ceremony at the United States Air Force Academy, just north of Colorado Springs in El Paso County, Colorado,