Initial results have suggested that they can reduce the level of the virus in the body and possibly shorten hospital stays when they are given early in the course of infection.

Friday afternoon Trump's physician wrote in a memo that he "remains fatigued but in good spirits".

The memo also said Melania Trump remains well with only a mild cough and headache, and the remainder of the first family is well and have tested negative.

Vice-President Mike Pence, second lady Karen Pence, Secretary of State Mike Pompeo and Treasury Secretary Steven Mnuchin have all tested negative. Republican National Committee Chairwoman Ronna McDaniel disclosed that she had tested positive.

Trump coming down with the virus means he will be temporarily off the campaign trail as he trails in the polls with barely a month to go before the Nov 3 election.

A fundraiser in Washington and a rally in Florida on Friday night were scrapped. Trump had planned to hold two rallies this weekend in Wisconsin, the White House coronavirus task force placing the state in the "red zone" because of its high rate of infections and recommended maximum social distancing there.

The second presidential debate, now scheduled for Oct 15, is in doubt. The vice-presidential debate is scheduled for next week.

The White House announcement that the president had tested positive resonated around the world quickly, provoking concern about this health, raising questions about his campaign for re-election just 32 days before the election and causing stock markets around the world to tumble at first but then recover.

The president's infection also comes amid his ongoing efforts to declare that the nation has largely moved past the worst threats of the pandemic, which has killed than 207,000 people in the US. Cases remain high or are rising in more than a dozen states. As recently as Thursday night Trump said in a recorded speech: "The end of the pandemic is in sight."