What treatment has the president received?

On Friday evening, Mr Trump's physician Sean Conley wrote in a memorandum: "I am happy to report the president is doing very well.

"He is 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."

Dr Conley said in a statement earlier on Friday that the president had "as a precautionary measure received an 8g dose of Regeneron's polyclonal antibody cocktail" at the White House.

The medication was administered to help reduce virus levels and speed recovery.

He was also taking zinc, vitamin D, famotidine, melatonin and aspirin, Dr Conley said.

"As of this afternoon he remains fatigued but in good spirits," he added.

The first lady, who is 50, was "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 Trumps' family, including the first couple's son Barron who also lives at the White House, tested negative.

How have Democrats reacted?

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.

Mrs Pelosi, who is also third in the presidential line of succession, was not notified in advance that the president would be taken to hospital, according to CBS.

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.

Who else in the president's orbit has tested positive?

In a fresh blow to his re-election campaign, Mr Trump's campaign manager reportedly tested positive for Covid-19 on Friday evening. Bill Stepien was said to be experiencing "mild flu-like symptoms", according to Politico.

Also on Friday, former White House counsellor Kellyanne Conway and Republican Senators Mike Lee and Thom Tillis announced they had tested positive.

All three attended Mr Trump's unveiling of his Supreme Court nominee, Judge Amy Coney Barrett, at the White House Rose Garden last Saturday.

Judge Coney Barrett tested positive for coronavirus earlier this year but has since recovered, unnamed officials told US media.

Republican National Committee Chairwoman Ronna McDaniel, who was with Mr Trump a week ago, has also tested positive, the party said on Friday.

On Thursday night, 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.

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 Ms Hicks' symptoms.

Officials said the process of tracking all Mr Trump's contacts in recent days was ongoing.

Several top White House aides have already tested positive in recent months for the virus including the vice-president's press secretary, Katie Miller, National Security Adviser Robert O'Brien and one of Mr Trump's personal valets.

BBC