WASHINGTON:U.S. President Donald Trump was in a military hospital on Saturday for treatment after testing positive for COVID-19, an extraordinary development that upended the presidential race a month before the Nov. 3 election.

Roughly 17 hours after he made his diagnosis public, Trump walked slowly from the White House to a waiting helicopter to be taken to Walter Reed National Military Medical Center in Bethesda, Maryland. He wore a mask and business suit and did not speak to reporters.

"I think I'm doing very well, but we're going to make sure that things work out," Trump said in a brief video message posted on Twitter. Early on Friday, he had tweeted that he and the first lady, Melania Trump, had contracted the virus.

Trump will work in a special suite at the hospital for the next few days as a precautionary measure, White House press secretary Kayleigh McEnany said. Online video showed a small group of Trump supporters outside Walter Reed late on Friday waving Trump 2020 flags, most not wearing masks.

Trump, 74, has a mild fever, according to a source familiar with the matter. White House doctor Sean P. Conley said late on Friday that Trump was doing very well, did not need supplemental oxygen, and had received a first dose of Remdesivir, an intravenous antiviral drug sold by Gilead Sciences Inc that has been shown to shorten hospital stays.

In a tweet late on Friday, the president wrote: "Going well, I think! Thank you to all. LOVE!!!"

The diagnosis was the latest setback for the Republican president, who is trailing Democratic rival Joe Biden in opinion polls ahead of the Nov. 3 presidential election.

Trump has played down the threat of the coronavirus pandemic from the outset, even as the disease has killed more than 200,000 Americans and hammered the U.S. economy.

A number of other prominent Republicans also tested positive on Friday, including former White House senior adviser Kellyanne Conway and Republican senators Mike Lee and Thom Tillis.

Vice President Mike Pence, who would take over presidential duties if Trump became severely ill, tested negative, a spokesman said. The former Indiana governor, 61, is working from his own residence several miles from the White House.

Trump is at high risk because of his age and weight. He has remained in apparent good health during his time in office but is not known to exercise regularly or to follow a healthy diet.

Conley said earlier on Friday that Trump has received an experimental treatment, Regeneron's REGN-COV2, one of several experimental COVID-19 drugs known as monoclonal antibodies, which are used for treating a wide range of illnesses.

Trump is also taking zinc, Vitamin D, famotidine, melatonin and aspirin, Conley said.

Stocks on Wall Street closed lower as news of Trump's diagnosis added to mounting uncertainties surrounding the election.

ELECTION DAY LOOMS

With just 31 days to go until Election Day, Trump's campaign said it would postpone rallies and other events where he was scheduled to appear, or take them online.

Trump's campaign manager, Bill Stepien, also tested positive for COVID-19 on Friday and will work from home, according to a senior campaign official.

Biden pulled ads attacking Trump off the air but otherwise continued his campaign, traveling to Michigan on Friday after testing negative for the virus.

At a union hall in Grand Rapids, Biden said he was praying for his rival's recovery. However, he also implicitly criticized Trump, who has mocked Biden for routinely wearing a mask and has held huge campaign rallies with little social distancing.

"Be patriotic," Biden said. "It's not about being a tough guy. It's about doing your part."

The Republican National Committee would choose a replacement nominee if Trump were to become incapacitated, but it is too late in most states to change the names on the ballot. Some 2.9 million people have already voted, according to figures compiled by University of Florida professor Michael McDonald.

Pence took over Trump's planned calls with governors and retirees' organizations. His Oct. 7 debate with Democratic vice presidential candidate Kamala Harris will go forward as planned, organizers said.

Harris has also tested negative, according to the campaign.

The virus could complicate Trump's push to install conservative judge Amy Coney Barrett on the Supreme Court.

In addition to the president and his wife, at least four people who were at a White House event to announce Barrett's nomination - Conway, Lee, Tillis and University of Notre Dame President John Jenkins - said Friday they have tested positive.

Lee and Tillis are both members of the Republican-controlled Senate Judiciary Committee, which is scheduled to begin hearings on Barrett's nomination on Oct. 12.

Barrett herself tested positive for the virus earlier this year and recovered, according to a person familiar with the matter.

Tillis, who said in a statement that he has no symptoms, will isolate at home for 10 days. Polls show a close race between him and Democratic challenger Cal Cunningham for his North Carolina seat, one of several Democrats hope to flip in their quest to win a Senate majority in November.

Trump is the latest world leader to contract the virus.

British Prime Minister Boris Johnson was rushed into intensive care after falling gravely ill in March. Brazilian President Jair Bolsonaro called the virus a "little flu" after being infected in July. Both men recovered.