US President Donald Trump has mild symptoms of coronavirus after he and his wife Melania tested positive for the illness, the White House says.
Mr Trump’s chief of staff said the president was “on the job” and “in good spirits”, adding that he expected him to make a quick recovery.
The news comes just over a month before presidential elections, where he will face Democratic challenger Joe Biden.
Other close members of Trump’s family have tested negative.
Officials said the process of tracking all the president’s contacts in recent days was ongoing. adding that Mr Trump was considering how he might address the nation or otherwise communicate with the American people on Friday.
On Thursday, the first couple said they intended to self-isolate after one of Mr Trump’s closest aides, Hope Hicks, tested positive. Soon afterwards they too received positive test results.
Ms Hicks, 31, travelled with Mr Trump on Air Force One to the first presidential TV debate with Mr Biden in Ohio on Tuesday. Some of Mr Trump’s family members who attended the debate were seen not wearing masks.
It has not been confirmed whether Mr Biden is also being tested, or if he will continue his campaign on Friday with a scheduled visit to Michigan. He stood approximately 10ft (3m) away from Mr Trump during the debate.
Mr Trump has mostly spurned mask-wearing and has often been pictured not socially distanced with aides or others during official engagements.
The coronavirus has infected more than 7.2 million Americans, killing more than 200,000 of them.
What do we know about Trump’s condition?
White House Chief of Staff Mark Meadows said Mr Trump was experiencing mild symptoms, but that he and Melania were “in good spirits”. He said he was optimistic the president would make a speedy recovery.
He was on the job and would remain on the job, Mr Meadows added, saying updates on his health were expected later on Friday.
Earlier Mr Trump wrote on Twitter: “We will get through this together.”
Mr Trump’s physician, Dr Sean Conley, released a statement late on Thursday, saying the president and the first lady were “both well at this time, and they plan to remain at home within the White House during their convalescence”.
According to Mr Trump’s most recent physical examination earlier this year, he weighed 244lbs (110.7kg). This is considered to be obese for his height of 6ft 3ins.
But Dr Conley stated at the time that the president “remains healthy”. Mr Trump will also have the best medical care available.
America’s Centers for Disease Control and Prevention (CDC) says a person must self-isolate for 10 days after a positive test.
It is not clear how Mr Trump’s positive test will affect arrangements for the second presidential debate, which is scheduled for 15 October in Miami, Florida.
Mr Trump is not the first world leader to have tested positive. Earlier this year, British Prime Minister Boris Johnson and Brazil’s President Jair Bolsonaro were infected. They both have since recovered, although Mr Johnson had to receive regular oxygen treatment to help his breathing during hospitalisation.
Is Mr Trump at particular risk because of his age?
It is dangerous to speculate about how the virus will affect any individual person.
There are clear risk factors – the older you are, the greater the risk of a coronavirus infection becoming life-threatening.
People aged 64-74 with Covid in the US are five times more likely to need hospital care and 90 times more likely to die than somebody in their 20s.
The CDC says eight out of 10 Covid deaths in the country have been in the over-65s.
The virus also seems to hit men and people who are overweight harder.
But that is the big picture – a pattern seen across the whole population – it is not a way of saying this is what will happen to the US president.
The health of any two 74-year-olds can be wildly different and other medical conditions massively alter how big a threat this virus poses.
Who else has been tested?
Vice-President Mike Pence and his wife were tested on Friday morning, and the results were negative, Mr Pence’s press secretary Devin O’Malley tweeted.
Later House Speaker Nancy Pelosi, who would in theory take charge of government if both the president and vice-president were incapacitated, said she had been tested on Friday morning and had not yet received the results.
Ms Pelosi, a Democrat, said “continuity plans were in place” but she herself had not been contacted by the White House about this.
Other members of the Trump family, his daughter Ivanka, son Barron and son-in-law Jared Kushner have all tested negative.
Several White House officials have been infected previously and the White House tests aides and anyone else who comes into contact with the president daily.
How have the US and the world reacted?
In a tweet, US Vice-President Mike Pence and his wife Karen wished the presidential couple well:
In a tweet, Mr Biden and his wife Jill wished the first couple a swift recovery: “We will continue to pray for the health and safety of the president and his family,” he said.
Boris Johnson wrote on Twitter: “My best wishes to President Trump and the First Lady. Hope they both have a speedy recovery from coronavirus.”
Other world leaders, including Indian Prime Minister Narendra Modi and his Israeli counterpart Benjamin Netanyahu, also sent messages of support to the couple.