US President Donald Trump plans to take part in next week's scheduled presidential debate with his Democratic rival Joe Biden despite his coronavirus diagnosis last week, a spokesman told Fox News late Monday.

"The president intends to debate," Tim Murtaugh told the broadcaster less than an hour after Trump left the Walter Reed medical centre, where he had been receiving treatment for Covid-19.

The second debate, during which the candidates are to answer questions from voters, is set to take place on October 15 in Miami.

There have been concerns that Trump may have been infectious at his first debate with Biden on Tuesday, when the pair stood two metres apart. Both men are in their 70s and in the high-risk category of those who become infected with coronavirus because of their age.

Biden has repeatedly tested negative for the virus in recent days and has said he is willing to take part in the next debate if health experts say it is safe to do so.

Guidelines from the US' Centers for Disease Control and Prevention say people with Covid-19 should self-isolate for at least 10 days after the onset of symptoms, but warn some people may remain infectious beyond that. Trump received his positive test on Thursday.

The Vice Presidential debate between Vice President Mike Pence and Democratic nominee Kamala Harris is to be held on Wednesday.