US President Donald Trump’s health has “continued to improve” as he is treated at the Walter Reed hospital near Washington for COVID-19, his doctors said Sunday, revealing he could be discharged as early as Monday.

His medical team said his blood oxygen levels had dropped twice briefly in recent days and he is being treated with steroids, but they gave an upbeat assessment of the 74-year-old’s president’s health and outlook.

“Since we spoke last, the president has continued to improve. As with any illness, there are frequent ups and downs over the course,” said Trump’s physician Sean Conley.

Trump and his wife First Lady Melania Trump, 50, tested positive for COVID-19 on Friday, a development that upended the Republican leader’s election campaign just weeks before the presidential polls on November 3.

Trump was flown to Walter Reed Military Medical Centre in Bethesda, a Maryland suburb of Washington DC, on Friday.

In a video posted late Saturday, Trump said he has started to “feel much better” and thanked the American people and global leaders for their support.

“I came here. Wasn’t feeling so well. I feel much better now. We’re working hard to get me all the way back. I have to be back because we still have to Make America Great Again,” Trump said in the video message from the military hospital in a suburb of Washington on Saturday.

President Trump is feeling “very well”, but will stay hospitalised, White House national security adviser Robert O’Brien said on Sunday.