THE White House said the president was “fatigued but in good spirits” and was taken to hospital as a precaution.
Mr Trump received an experimental drug cocktail injection at the White House after he and First Lady Melania Trump both tested positive for Covid-19.
It is a potential setback as he trails Democratic challenger Joe Biden a month before the presidential election.
Wearing a mask and suit, Mr Trump walked out across the White House lawn on Friday afternoon to his helicopter, Marine One, for the short flight to Walter Reed National Military Medical Center in the Washington DC suburbs.
He waved and gave a thumbs-up to reporters but said nothing before boarding the aircraft.
In a video posted to Twitter, Mr Trump said: “I think I’m doing very well. But we’re going to make sure that things work out. The first lady is doing very well. So thank you very much.”
White House press secretary Kayleigh McEnany said in a statement: “President Trump remains in good spirits, has mild symptoms, and has been working throughout the day.
“Out of an abundance of caution, and at the recommendation of his physician and medical experts, the president will be working from the presidential offices at Walter Reed for the next few days.
“President Trump appreciates the outpouring of support for both he and the first lady.”