President Joe Biden will transfer power briefly to Vice-President Kamala Harris while he is under anaesthesia for a routine colonoscopy, making her the first woman to hold presidential power in US history.

Biden, a Democrat, is undergoing his annual physical at the Walter Reed military hospital outside of Washington.

Harris is the first woman to serve as vice-president of the US; no woman has ever been President in the country’s nearly 250-year history.

“Following the process set out in the Constitution, President Biden will transfer power to the Vice-President for the brief period of time when he is under anaesthesia,” White House spokesperson Jen Psaki said in a statement.

“The Vice-President will work from her office in the West Wing during this time,” Psaki said.

Biden arrived at Walter Reed just before 9am (1400 GMT) on Friday; Harris is expected to depart for Ohio, where she’s promoting the infrastructure bill, in the early afternoon.

Presidential power has been transferred to the vice- president before, when President George W. Bush had colonoscopies in 2002 and 2007.

Biden, who turns 79 on Saturday, is the oldest person to take office as US President, leading to high interest in his health and well-being. Although speculation has persisted about whether he will run for re-election in 2024, he has said he expects to seek a second four-year term.

Biden has pledged to be more transparent about his health than predecessor Donald Trump.