President Joe Biden tested positive for Covid-19 on Wednesday, the White House said.

The president, who was delivering speeches in Las Vegas, "is experiencing mild symptoms," White House press secretary Karine Jean-Pierre said in a statement.

Biden "will be returning to Delaware where he will self-isolate and will continue to carry out all of his duties fully during that time," Jean-Pierre said.

Biden is vaccinated and boosted, she noted.

"The White House will provide regular updates on the President's status as he continues to carry out the full duties of the office while in isolation," she said.

Biden boarded Air Force One in Las Vegas around 6:30 p.m. ET, the White House pool reported. The president was not wearing a mask as he boarded the plane.

"Good, I feel good," Biden told reporters in response to shouted questions on the airport tarmac.

Biden's doctor said that the president came down with a runny nose and a "non-productive cough" on Wednesday afternoon.

"He felt okay 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," the physician said in a statement shared by the White House.

Biden's symptoms "remain mild," with a normal temperature and respiratory rate and a 97% pulse oximetry reading, according to the doctor.

"The President has received his first dose of Paxlovid," the physician said. "He will be self-isolating at his home in Rehoboth."

The Biden campaign referred CNBC to the White House when asked for comment.

Biden was scheduled to deliver remarks Wednesday afternoon at the UnidosUS Annual Conference in Las Vegas, after an interview with Univision at the Original Lindo Michoácan Restaurant.

Photos show Biden shaking hands with patrons at that restaurant.

But Biden did not show up to the conference at his scheduled speaking time of 4:30 p.m. ET.

After 6 p.m. ET, UnidosUS President Janet Murguia announced to the crowd that Biden had tested positive for the virus.

"Regrettably, I was just on the phone with President Biden, and he shared his deep disappointment at not being able to join us this afternoon," she said. "The president has been at many events, as we all know, and he just tested positive for Covid."

"He said to tell my folks that we're not going to get rid of him that quickly," she added. "He's just really sorry he couldn't be with us."

The illness comes as Biden, 81, has come under mounting pressure from his fellow Democrats to withdraw from the presidential race against Republican nominee Donald Trump.

A growing number of Democratic lawmakers, along with top donors and other allies, have urged Biden to step aside after his disastrous debate performance stoked panic about his fitness to campaign.

Biden has repeatedly rejected those calls and defended his physical and mental health.

But in an interview with BET on Tuesday, Biden said that he might reconsider his decision to stay in the race if a "medical condition" emerged.

Biden previously tested positive for Covid in July 2022.

The Biden campaign quickly tried to turn his latest bout of the virus into a fundraising opportunity — and a dig at Tesla and SpaceX CEO Elon Musk, who has reportedly pledged to donate heavily to a pro-Trump super PAC.

Biden's personal X account on Wednesday evening shared a thread beginning with a two-word post: "I'm sick."

But the next post read, "of Elon Musk and his rich buddies trying to buy this election." That post included a link to the Biden campaign's fundraising page.