U.S. President Donald Trump participates in the first presidential debate against Democratic presidential nominee Joe Biden at the Health Education Campus of Case Western Reserve University on September 29, 2020 in Cleveland, Ohio. (Getty/Kyodo)

WASHINGTON - U.S. President Donald Trump was hospitalized on Friday "out of an abundance of caution," the White House said, hours after his revelation of his diagnosis with the novel coronavirus sent a jolt through the country with just a month to go to the presidential election.

The 74-year-old leader's arrival at Walter Reed National Military Medical Center near Washington to stay "for the next few days" came after he revealed his positive test result in a tweet in the early hours of Friday.

Trump, whose diagnosis takes him off the campaign trail and upends a campaign strategy that has focused on in-person rallies, gave a thumbs-up and a short wave to reporters as he left the White House to travel to the military medical center by helicopter. He was seen wearing a mask.

"I think I'm doing well, but we're going to make sure that things work out," Trump said in an 18-second video message posted on Twitter. He said his wife Melania, 50, who also tested positive, is "doing very well" and expressed gratitude for the support they are receiving.

"I appreciate it. I will never forget. Thank you," he said.

Earlier in the day, the president's physician Sean Conley said that Trump "remains fatigued but in good spirits" while Melania remains well with a mild cough and headache.

Conley said Trump has received a dose of an experimental antibody cocktail manufactured by Regeneron Pharmaceuticals Inc. as a "precautionary measure."

Democratic presidential nominee Joe Biden, the 77-year-old former vice president who faced off with Trump in the first presidential debate on Tuesday, tweeted that he and his wife Jill have tested negative, while wishing the Trumps a "swift recovery."

"I hope this serves as a reminder: wear a mask, keep social distance, and wash your hands," Biden said.

The development comes as Trump has faced criticism over his handling of the coronavirus pandemic, which has infected more than 7.3 million people and killed 208,000 in the United States, with both figures higher than in any other country in the world.

He has repeatedly downplayed the threat of the virus, telling the public to stay calm because the virus would just "go away," while holding in-person campaign rallies in recent months to galvanize his support base.

The Trump campaign said Friday that all previously announced campaign events involving the president are "in the process of being moved to virtual events or are being temporarily postponed."

The move is a blow to Trump, who has trailed Biden in national polls and is running out of time to turn the tide.

Meanwhile, the campaign said that Vice President Mike Pence plans to attend scheduled campaign events as he has tested negative for the virus.

A debate between Pence and Democratic vice presidential nominee Kamala Harris, who also tested negative, will take place in Utah next Wednesday as scheduled, U.S. media said, citing remarks from the Commission on Presidential Debates.

Trump and Biden have two more scheduled debate events on Oct. 15 and Oct. 22, but it was not clear whether they will be affected.

Democratic presidential nominee Joe Biden participates in the first presidential debate against U.S. President Donald Trump at the Health Education Campus of Case Western Reserve University on September 29, 2020 in Cleveland, Ohio. (Getty/Kyodo)

During Tuesday's first debate, Trump mocked Biden for regularly wearing a mask.

"Every time you see him, he's got a mask. He could be speaking 200 feet away from me, and he shows up with the biggest mask I've ever seen," Trump said, while insisting that he would wear a mask when needed.

Trump has been seen wearing a mask on only a handful of occasions, despite calls for leaders to set an example for the public. Critics have speculated that Trump's reluctance to wear a mask may stem from a desire to avoid looking "weak" and maintain the image of a tough leader.

Trump was found to have contracted the virus after Hope Hicks, a counselor to the president, tested positive on Thursday. She had reportedly traveled with Trump several times this week aboard Air Force One.

In the wake of Trump's diagnosis, Cabinet members and others reported their test results.

Pence and his wife Karen, as well as Secretary of State Mike Pompeo, who is traveling abroad and plans to head to Japan and other Asian countries from Sunday, all tested negative.

Defense Secretary Mark Esper has also been away from the United States but had tested negative for the virus earlier this week in preparation for and as part of his overseas trip, according to the Defense Department.

Among the leaders of the Group of Seven industrialized nations, British Prime Minister Boris Johnson also contracted the virus. He recovered and returned to work in late April, after being hospitalized for about three weeks.

White House Counselor Hope Hicks, White House Deputy Chief of Staff for Communications and Director of Social Media Dan Scavino, White House Chief of Staff Mark Meadows and White House Staff Secretary and Counsel to the President Derek Lyons walk on the South Lawn after President Donald Trump returned to the White House from a trip to Michigan May 21, 2020 in Washington, DC. (Getty/Kyodo)