WASHINGTON - President Donald Trump will stay at a military hospital outside Washington DC for a few days as a precautionary measure following his Covid-19 diagnosis on Friday (Oct 2), the White House said.

His physician Sean Conley said that Mr Trump "remains fatigued but in good spirits" as of Friday afternoon, while his wife Melania, who also tested positive for Covid-19, remained well with only a mild cough and headache.

Mr Conley said Trump has received an experimental treatment, Regeneron's REGN-COV2, Reuters reported.

The drug is one of several experimental Covid-19 drugs known as monoclonal antibodies, which are used for treating a wide range of illnesses.

US infectious disease chief Dr Anthony Fauci is among those saying the technology has promise.

Mr Trump is also taking zinc, Vitamin D, famotidine, melatonin and a daily aspirin.

The President was uncharacteristically silent on Twitter for most of the day after announcing his diagnosis, but in his first public comments in the evening, said he believes he is "doing very well".

"I want to thank everybody for the tremendous support," said Mr Trump in a brief video message on Twitter, posted around the time he arrived by helicopter at the Walter Reed National Military Medical Center in Bethesda, Maryland.

"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," he said, dressed in a suit and blue tie.

He thanked well wishers for their support, adding: "Thank you very much, I appreciate it, I will never forget it."

In a memorandum released to the media, Dr Conley said that the President received a single 8 gram dose of biotech company Regeneron's antibody cocktail, and completed the infusion without incident.

The President has also been taking zinc, vitamin D, famotidine, melatonin and a daily aspirin, he added.

Earlier in the day, Press Secretary Kayleigh McEnany said that Mr Trump remained in good spirits with mild symptoms, and had been working throughout the day.

"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 in a statement.

"President Trump appreciates the outpouring of support for both he and the First Lady," she added.

According to media pool reports, Mr Trump gave a thumbs-up to reporters and a short wave as he left the White House to board the Marine One helicopter to head to the hospital.

Wearing a mask, he walked normally on his own without any outward sign of trouble, said the pool report.

Former president Barack Obama sent a message of support to Mr Trump and his wife Melania at the start of a fund-raising event with vice-presidential candidate Kamala Harris.

"Although we're in the midst of a big political fight, and we take that very seriously, we also want to extend our best wishes to the president of the United States, the First Lady," Mr Obama said.

"Michelle and I are hopeful that they and others that have been affected by Covid-19 around the country are getting the care that they need, that they are going to be on the path to a speedy recovery." he said.

"We're all Americans and we're all human beings, and we want to make sure everybody is healthy."

The Trumps' 14-year-old son Barron, Vice-President Mike Pence and Democratic presidential candidate Joe Biden all tested negative for the virus.

While the impact of the diagnosis on the race is uncertain, Mr Trump's quarantine forces him off the campaign trail for now, a blow to his efforts to drum up support at in-person events at a time when he is trailing Mr Biden by seven points nationally.

Mr Trump was due to meet Mr Biden on Oct 15 in Miami, Florida and Oct 22 in Nashville, Tennessee for the second and third presidential debates, which are now up in the air.

Responding on Friday, Mr Biden, who debated Mr Trump at an indoor venue in Cleveland, Ohio, on Tuesday, said on Twitter: "(My wife) Jill and I send our thoughts to President Trump and First Lady Melania Trump for a swift recovery. We will continue to pray for the health and safety of the president and his family."

In a lunchtime poll of 1,000 Americans on Friday, Morning Consult and the Politico news outlet found that just under half are more worried about the economy following Mr Trump's coronavirus diagnosis.

Some 56 per cent say they disapprove of the way Mr Trump has handled the coronavirus pandemic, compared with 41 per cent who approve.

Most - 53 per cent - also say they are at least somewhat more likely to wear a face mask and to practise social distancing, after they heard that Mr Trump had tested positive on Friday.

Meanwhile, former White House counsellor Kellyanne Conway said on Friday night (Oct 2) that she had tested positive for the coronavirus.

"My symptoms are mild (light cough) and I'm feeling fine. I have begun a quarantine process in consultation with physicians," Conway, who left the White House in August, said on Twitter.

She did not say how she might have contracted the virus but she had attended the ceremony at the White House last Saturday for Trump's announcement that he would nominate Judge Amy Coney Barrett to replace the late Ruth Bader Ginsburg on the Supreme Court, Bloomberg reported.

Two Republican senators, Thom Tillis of North Carolina and Mike Lee of Utah, who also attended the event, had contracted the virus.