U.S. President Donald Trump, who's staying at a military hospital for COVID-19 treatment, said Saturday he is feeling "much better" while calling the comings days "real test" for his condition.

"I came here, wasn't feeling so well. I feel much better now, we're working hard to get me all the way back," Trump said in a four-minute video clip posted on Twitter. "I think I'll be back soon."

"I look forward to finishing up the campaign, the way it was started and the way we've been doing," said the president, who's seeking a second term.

In the video, Trump is seen sitting behind a desk, wearing a blue jacket and a white shirt with the collar button undone.

"Over the next period of a few days, I guess that's the real test," he said. "So we'll be seeing what happens over those next couple of days."

Trump also said his wife, Melania, who had also tested positive for COVID-19 and is in quarantine at the White House, "is doing very well."

"Melania is really handling it very nicely," he continued. "And that makes me very happy."

Trump was first diagnosed with COVID-19 on Thursday before moving to Walter Reed National Military Medical Center in Bethesda, Maryland on Friday evening, where he is using Remdesivir, a COVID-19 drug made by U.S. biopharmaceutical company Gilead Sciences, as a treatment.

A source familiar with the president's health told reporters on Saturday that the next 48 hours will be critical for the president after doctors said he is doing well.

"The president's vitals over the last 24 hours were very concerning," the source said in comments passed along to the media by a member of the White House press pool. "The next 48 hours will be critical in terms of his care. We're still not on a clear path to a full recovery."

The statement came shortly after White House physician Sean Conley said Saturday morning that Trump is "doing very well".