Minutes after the announcement, the president’s motorcade was on the move from taping a radio interview in Las Vegas to the Las Vegas airport.
Biden boarded Air Force One and told reporters travelling with him, “I feel good.”
The White House said Biden planned to spend a long weekend at his Delaware beach house. It was unclear how long the sickness would keep him from the campaign trail.
Biden had earlier greeted a couple of dozen people at a Mexican restaurant prior to going behind closed doors for the interview.
Dr Kevin O’Connor, the president’s physician, said in a note that Biden “presented this afternoon with upper respiratory symptoms, to include rhinorrhea (runny nose) and non-productive cough, with general malaise.”
After the positive COVID-19 test, Biden was prescribed the antiviral drug Paxlovid and has taken his first dose, O’Connor said.
“He felt OK for his first event of the day, but given that he was not feeling better, point of care testing for COVID-19 was conducted and the results were positive for the COVID-19 virus,” a White House statement said.
Biden has been vaccinated and is currently on his recommended annual booster dose for COVID-19.
When Biden was late for the start of a conference for Latino civil rights organisation UnidosUS, where he had been scheduled to speak on Wednesday afternoon, the organiser announced he had tested positive.
Biden spent two nights in Vegas on the campaign trail.
The president is locked in a battle with some fellow Democrats who worry he is too old to seek re-election and want him to step aside in favour of another candidate.
He has been defiant in the face of the calls to quit the race, telling one interviewer that only the “Lord Almighty” could persuade him to go.
He suffered a blow earlier on Wednesday when a prominent Democratic member of the US House of Representatives, Adam Schiff of California, said it was time for Biden to “pass the torch” to someone else.
US Senate Democratic leader Chuck Schumer told Biden in a meeting on Saturday it would be better for the country and the Democratic Party if he ended his re-election campaign.
Jean-Pierre said the president would continue working from isolation.
“He will be returning to Delaware where he will self-isolate and will continue to carry out all of his duties fully during that time.”
Biden last tested positive for COVID-19 twice in the summer of 2022, when he had a primary case and a rebound case of the virus.
US health officials have reported recent upticks in emergency room visits and hospitalisations from COVID-19.
There has also been a pronounced increase in positive test results in much of the country, particularly in the southwest.
