WASHINGTON - US President Donald Trump was discharged from the hospital on Monday (Oct 5) evening after being treated there for Covid-19 over the weekend, promising that he would be back on the campaign trail soon, although his doctors said that he is not yet out of the woods.

Mr Trump walked out of the Walter Reed National Military Medical Centre entrance without any assistance on Monday evening around 6.30pm, pumping his fist twice and giving a thumbs-up.

He declined to answer questions shouted out by the media, including how many White House staff were ill and whether he was a super spreader, before boarding a vehicle that took him to the Marine One helicopter, which brought him back to the White House.

Once back at the White House, he walked up the South Portico stairs, removed his mask and gave another thumbs-up, saluting Marine One twice before going inside.

"He's back," said the president's physician Sean Conley at a press briefing on Monday, soon after Mr Trump announced his imminent discharge on Twitter.

"Though he might not be entirely out of the woods yet, the team and I agree that all our evaluations and, most importantly, his clinical status support the president's safe return home, where he'll be surrounded by world-class medical care," said Dr Conley.

Mr Trump's doctors said that he had "met or exceeded all discharge criteria" and that it had been more than 72 hours since his last fever.

"We're in a bit of uncharted territory when it comes to a patient who received the therapies he has so early in the course," Dr Conley said.

"So we're looking to this weekend. If we can get through to Monday with him remaining the same or improving, better yet, then we will all take that final deep sigh of relief," he said, adding that the doctors remained cautiously optimistic and on guard.

Mr Trump will receive a fourth dose of Remdesivir before returning to the White House, where he will receive his fifth and final dose on Tuesday, said the doctors. He will also remain on the steroid dexamethasone.

Mr Trump, whose Covid-19 diagnosis was announced early Friday morning, had been hospitalised since Friday evening at the Walter Reed National Military Medical Centre outside Washington DC.

"Don't be afraid of Covid. Don't let it dominate your life. We have developed, under the Trump Administration, some really great drugs & knowledge. I feel better than I did 20 years ago!" said the President on Twitter on Monday.

Dr Conley declined to comment on what the President had said. But Mr Trump's downplaying of the pandemic, which has infected nearly 7.6 million Americans and killed around 210,000 of them, alarmed medical experts.

Council on Foreign Relations global health director Tom Bollyky said on Twitter that was "not the obvious lesson to draw from a three-day hospitalisation of a US President, an experimental drug having to be given to save him and an outbreak that has now engulfed White House staff and associates".

Since testing positive, Mr Trump had experienced two episodes of a drop in oxygen, one on Friday morning before he went to the hospital and again on Saturday, according to his doctors at the press briefing on Sunday.

On Twitter, Mr Trump also responded against criticism following his unscheduled drive-by on Sunday evening, when he left the hospital in an armoured car to wave to his supporters waiting outside the hospital.

Medical experts had said that Mr Trump had put the driver and the Secret Service agent accompanying him in danger of contracting the virus from him, as the vehicle interior was a small airtight space.

"It is reported that the Media is upset because I got into a secure vehicle to say thank you to the many fans and supporters who were standing outside of the hospital for many hours, and even days, to pay their respect to their President," said Mr Trump on Twitter. "If I didn't do it, Media would say RUDE!!!"

Responding to questions on Mr Trump's Sunday excursion, Dr Conley said that the president had been surrounded by medical and security staff for days wearing full personal protective equipment.

A question mark also hung over whether the President could return to the campaign trail, given concerns that he might infect others with the coronavirus. "As far as travel goes, we'll see," said Dr Conley.

But Mr Trump appeared to be eager to return to campaigning, particularly as several polls released after the presidential debate last week showed Democratic presidential nominee Joe Biden widening his lead over Mr Trump.

Said the President on Twitter on Monday evening, shortly before he left the hospital: "Will be back on the Campaign Trail soon!!! The Fake News only shows the Fake Polls." Mr Biden said on Twitter: "Now that President Trump is busy tweeting campaign messages, I would ask him to do this: Listen to the scientists. Support masks. Support mask mandates nationwide."