Trump transported to Walter Reed hospital after COVID-19 diagnosis

President Donald Trump, who has COVID-19, will be flown to Walter Reed National Military Medical Center Friday afternoon in his helicopter as a precautionary measure, the White House said Friday.

The move was recommended by the president’s physician, Press Secretary Kayleigh McEnany said, and he is expected to remain at the military hospital for several days. He will work from the presidential offices there, McEnany said.

He left the White House shortly after 6:15 p.m. ET and arrived at the hospital in Bethesda, Maryland, minutes later after the short helicopter flight on Marine One.

Three people familiar with his condition said earlier Friday Trump has a low-grade fever. The president’s doctor said he was administered an antibody cocktail, along with vitamins, and is fatigued, while Melania Trump has a mild cough and headache.

Earlier, administration officials said Trump was experiencing "mild symptoms" after he announced early Friday that he tested positive for the disease.

But Trump, who regularly posts on Twitter, was silent on the social media platform after announcing his infection and ceded the only event on his official public schedule to Vice President Mike Pence.

Trump, who is 74 and clinically overweight, is at a higher risk of complications from the virus, due to his age and weight, according to guidance from the Centers for Disease Control and Prevention. The risk of a severe illness increases with age and other factors, and other medical conditions can also increase risk, including obesity, according to the agency.

Trump weighs about 240 pounds and is about 6 feet, 3 inches tall, according to past health assessments made public in June. His physician has said he is overall healthy.

Vice President Mike Pence, who tested negative for the disease on Friday, remained at the vice presidential residence at the Naval Observatory, according to a senior administration official.

Presidential power has not been transferred to the vice president, White House communications director Alyssa Farah told NBC News.

“The president is in charge," she said.

Marine One landed on the White House South Lawn shortly before 5:30 p.m. ET. A small group of senior White House staff gathered outside for the departure. Trump, wearing a suit and a face mask, was seen walking to the helicopter. Trump waved to reporters before boarding. Moments later, he was seen disembarking from the helicopter on the Walter Reed grounds. He was accompanied by his chief of staff Mark Meadows and was not accompanied by the first lady.

In an 18-second taped video posted to Twitter moments after he touched down near the hospital, Trump said, “I think I’m doing very well, but we’re going to make sure that things work out."

Three people familiar with his condition said earlier Friday Trump has a low-grade fever. The president’s doctor said he was administered an antibody cocktail, along with vitamins, and is fatigued, while Melania Trump has a mild cough and headache.

The experimental drug provided to the president is a combination of two so-called monoclonal antibodies and is meant to provide the body's immune system with a temporary, but immediate, boost to fight off the coronavirus.

Regeneron, which makes the drug, confirmed to NBC News that it provided it to the president under what is called "compassionate use," through which Food and Drug Administration allows access to experimental drugs outside of clinical trials for patients with a life-threatening condition or serious disease.

Meanwhile, Joe Biden, who tested negative for COVID-19 earlier Friday, said during a campaign stop in Grand Rapids, Michigan, that Trump’s positive test required the U.S. to take the virus seriously and follow safety protocols rigorously.

“We need to take the science of fighting this disease seriously if we're going to save lives. And above all, the news is a reminder that we as a nation need to do better in dealing with this pandemic,” Biden said, after offering his prayers to Trump and first lady Melania Trump, who also tested positive Friday.

Biden, who shared a stage with Trump in Cleveland on Tuesday for the first presidential debate, said the moment called for putting politics aside and acknowledging the gravity of the virus — and for wearing a mask.

“These face masks are the most important, powerful public health tool we have,” said Biden, who himself never removed his blue surgical mask during his remarks.

A Biden campaign official told NBC News that the campaign is pulling all of its negative advertising from their rotation of paid media.

Related: Trump's age and weight have doctors worried the president is at risk for severe complications.

Trump's handling of the coronavirus pandemic has been a central point of the election, with his opponents criticizing his response. Trump, who has been accused of downplaying the risk and severity of the pandemic, mocked Biden's regular use of masks during Tuesday's debate and defended his record on responding to the virus. Public health experts have said the mixed messaging hampered the country's response to the pandemic and even led to preventable deaths.

Biden and Trump, however, stood more than 12 feet away from each other during the debate, according to the Commission on Presidential Debates — well beyond the six feet of social distance recommended by the CDC.

But in a sign that safety measures at the debate, hosted by the Cleveland Clinic, may not have been air-tight, at least 11 positive coronavirus tests can be traced to organizers of this week's presidential debate in Cleveland, city officials said Friday.

Trump's transport to the hospital, coming as dual public health and economic crises continue to ravage the U.S, throws into further chaos in the final month of the presidential campaign.

The sole vice presidential debate, however, will proceed as planned in Salt Lake City, on Wednesday. Biden’s running mate, Sen. Kamala Harris, D-Calif., and her husband both tested negative on Friday, aides to Harris told NBC News.

It's also spurred grim chatter over what happens when a president is, for any reason, unable to carry out the duties of the office. Under a provision of the Constitution, the vice president would become the acting president. But if both the president and the vice president become incapacitated, the Presidential Succession Act dictates that House speaker, now Democrat Nancy Pelosi of California, followed by the president pro tem of the Senate, who is now Republican Chuck Grassley of Iowa, are the next in line to serve as acting president.

Pelosi, for her part, said she was not informed of Trump's planned movement to Walter Reed and has not had any further conversations about the continuity of government planning with the White House in the intervening hours, according to a Democratic aide.

A spokesman for Grassley, meanwhile, responded to questions over whether he'd been notified of Trump's transport to Walter Reed by saying, “Generally, continuity of government briefings are not made public.”

This story originally appeared on NBCNews.com.

Hallie Jackson and Shannon Pettypiece reported from Washington. Adam Edelman reported from New York.