Joe Biden has tested positive for Covid-19 and is suffering mild symptoms, the White House has said.
Karine Jean-Pierre, his press secretary, said the US president is vaccinated and boosted. He has tested positive for Covid twice before, reports BBC.
Biden, 81, was seen earlier on Wednesday visiting supporters in Las Vegas and speaking at an event. He has cancelled a campaign speech later in the night.
The illness comes as he faces increasing pressure to step aside because of his age.
US media reports both Senate Majority Leader Chuck Schumer and House Majority Leader Hakeem Jefferies - the top two Democrats in the US Congress - separately met with Biden privately and expressed that there is deep concern his candidacy could negatively impact other House and Senate races.
Jean-Pierre said the president planned to isolate at his home in Delaware while he carries out "all of his duties fully during that time".
The president's doctor, Kevin O'Connor, said Biden presented with upper respiratory symptoms, including a runny nose and a cough and was given his first dose of Paxlovid.
He felt fine during his first event of the day, but later tested positive Dr O'Connor said.
Biden later used X/Twitter to thank everyone for "the well wishes" and said he would "work to get the job done for the American people" while in recovery.
In another tweet his account stated: "I'm sick", before replying back: "... of Elon Musk and his rich buddies trying to buy this election. And if you agree, pitch in here."
The tweet pointed to a donations portal.
Reporters on the Las Vegas trip said they were rushed to the city's airport following the announcement.
Biden moved slowly and cautiously up the steps to the plane, video shows. He was not wearing a mask.
As he boarded Air Force One he was heard to say: "Good, I feel good."
