U.S. President Donald Trump arrives at Walter Reed National Military Medical Center, Oct. 2, following a White House announcement that he "will be working from the presidential offices at Walter Reed for the next few days" after testing positive for COVID-19. Reuters-Yonhap

U.S. President Donald Trump was moved to a military hospital for treatment on Friday after being diagnosed with COVID-19 as his administration and re-election campaign scrambled to adjust to an extraordinary twist in his turbulent presidency.

Roughly 17 hours after he announced he had tested positive for the coronavirus, 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 posted on Twitter.

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.

Trump, 74, has a mild fever, according to a source familiar with the matter. White House doctor Sean P. Conley said he is being treated with an experimental drug cocktail and is "fatigued but in good spirits."

It 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, who has played down the threat of the coronavirus pandemic from the outset, wrote on Twitter earlier Friday that he and his wife Melania were going into quarantine after testing positive for the virus, which has killed more than 200,000 Americans and severely damaged the U.S. economy.

An active Twitter user, Trump has posted only the short video since then.

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 Trump has received an experimental treatment, Regeneron's REGN-COV2. The drug is one of several experimental COVID-19 drugs known as monoclonal antibodies, which are used for treating a wide range of illnesses. U.S. infectious disease chief Dr. Anthony Fauci is among those saying the technology has promise.

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

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