A feverish US President Donald Trump has been flown to hospital after testing positive for coronavirus.
His doctor said Mr Trump was “fatigued but in good spirits” and, in a later update, that he was doing well.
Mr Trump has so far been treated with an experimental drug cocktail injection and the antiviral medication Remdesivir after both he and First Lady Melania Trump tested positive for Covid-19.
In exactly one month, Mr Trump faces Joe Biden in the presidential election.
The president’s diagnosis has upended his campaign and also cast doubt on his attempt to get a new Supreme Court judge confirmed before polling day.
The latest update from Mr Trump’s physician, Sean Conley, in a memorandum late on Friday, read: “I am happy to report the president is doing very well.” He said the president was not in need of supplemental oxygen.
Mr Trump is expected to be in hospital for the “next few days”.
The list of other people to have tested positive around Mr Trump include close aide Hope Hicks – believed to be the first to show symptoms – campaign manager Bill Stepien and former White House counsellor Kellyanne Conway. Republican Senators Mike Lee and Thom Tillis have also tested positive.
Wearing a mask and suit, Mr Trump walked out across the White House lawn on Friday at 18:15 (22:15 GMT) to his helicopter, Marine One, for the short flight to Walter Reed National Military Medical Center in the Washington DC suburbs.
He waved and gave a thumbs-up to reporters but said nothing before boarding the aircraft.
In an 18-second video posted to Twitter, Mr Trump said: “I think I’m doing very well. But we’re going to make sure that things work out. The first lady is doing very well. So thank you very much.”
The president’s children, Ivanka and Eric, retweeted his post, praising him as a “warrior”. Ms Trump added: “I love you dad.”
Donald Jr said his father was “obviously taking it very seriously”.
Mr Trump was admitted to the presidential suite at Walter Reed, which is where US presidents usually have their annual check-up.
Shortly before midnight, he tweeted again: “Going well, I think! Thank you to all. LOVE!!!”
Mr Trump’s symptoms include a low-grade fever, according to the BBC’s US partner CBS News.
His doctor, Sean Conley, said the president was “not requiring any supplemental oxygen, but in consultation with specialists we have elected to initiate Remdesivir therapy. He has completed his first dose and is resting comfortably”.
Tests have shown Remdesivir, originally developed as an Ebola treatment, disrupts the virus’s ability to duplicate and can cut the duration of symptoms.
Earlier on Friday, Dr Conley said the president had “as a precautionary measure received an 8g dose of Regeneron’s antibody cocktail” at the White House.
The antibodies stick to the coronavirus, protecting the body’s cells and making the virus more visible to the immune system.
However, the treatment it is still experimental and has not yet been approved by regulators. Although there is a lot of hope behind it, some doctors have expressed concern at its use on the president at this stage.
Mr Trump was also taking zinc, vitamin D, famotidine, melatonin and aspirin, Dr Conley said.
The president, being 74, a man and someone categorised as obese, is in a higher-risk category for Covid-19.
The first lady, who is 50, was said to be “well with only a mild cough and headache”.
On Friday afternoon, Mrs Trump said she was experiencing mild symptoms but was “feeling good” and “looking forward to a speedy recovery”.
The remainder of the Trump family, including the first couple’s son Barron, who also lives at the White House, tested negative.
White House press secretary Kayleigh McEnany said President Trump had been in good spirits and worked throughout the day on Friday.
“Out of an abundance of caution, and at the recommendation of his physician and medical experts, the president will be working from the presidential offices at Walter Reed for the next few days,” she said.
“President Trump appreciates the outpouring of support for both he and the first lady.”
White House communications director Alyssa Farah said the president had not transferred his powers to Vice-President Mike Pence.
“The president is in charge,” she said.
But he pulled out of a video conference call with vulnerable seniors scheduled for Friday, leaving Mr Pence to chair the meeting.
Under the US constitution, if Mr Trump did become too ill to carry out his duties, he could hand over his powers to the vice-president temporarily.
Under such a scenario Mr Pence – who tested negative for Covid-19 on Friday – would become acting president until Mr Trump was fit again and could resume work.
Analysis by Peter Bowes, BBC North America correspondent
This is a crisis that’s escalating by the hour.
With the news that another member of Trump’s inner circle, Kellyanne Conway, has tested positive, along with two Republican senators, there’s a growing realisation that a Covid cluster has penetrated the heart of US government.
Like Ms Conway, Senators Mike Lee of Utah and Thom Tillis of North Carolina attended the White House event where the president announced his nomination of Amy Coney Barrett to the Supreme Court.
Four other attendees are also known to have tested positive.
Chuck Schumer, the Democratic leader in the Senate, said it would be “irresponsible and dangerous” to move forward with Amy Coney Barrett’s confirmation hearings.
It would be another huge blow to the president if the proceedings were delayed, although Senate leader Mitch McConnell has said they will continue with expanded use of remote hearings.
Mr Biden, the Democratic nominee, and his wife Jill tested negative on Friday. The Bidens wished the presidential couple a speedy recovery.
Mr Biden said on the campaign trial in Grand Rapids, Michigan, on Friday: “Be patriotic. It’s not about being a tough guy. It’s about doing your part.”
The Republican president poked fun at Mr Biden during their live TV debate on Tuesday, saying: “I don’t wear masks like him. Every time you see him, he’s got a mask.”
The Democrat’s campaign said it was in the process of temporarily taking down all its negative ads regarding Mr Trump.
Speaking at a virtual campaign event for Mr Biden, former President Barack Obama also extended well wishes to Mr and Mrs Trump.
“We’re all Americans and we’re all human beings and we want to make sure everybody is healthy,” he said.
The most powerful elected Democrat, House of Representatives Speaker Nancy Pelosi, said her prayers for Mr Trump had “intensified” after his positive coronavirus test.
The California congresswoman – who is one of Mr Trump’s foremost political antagonists – said she hoped his diagnosis would be “a learning experience” for the country.
Since the onset of the pandemic, Democrats have criticised the president for flouting basic health guidelines, such as social distancing and wearing a facial covering in public – including those promoted by his own administration. Mr Trump has also continued to hold large campaign rallies, gathering thousands of supporters, often without masks.
There has been criticism of the president’s decision to go to a fundraiser attended by dozens of people in New Jersey on Thursday, apparently when officials already knew about Hope Hicks’ symptoms.
Officials said the process of tracking all Mr Trump’s contacts in recent days was ongoing.