United States President Donald Trump on Thursday rejected plans to hold his next debate with Democratic rival Joe Biden virtually to reduce the risk of spreading Covid-19, complaining that his microphone could be cut off in that format.

The first debate between the two, held last week before Trump disclosed that he had tested positive for the novel coronavirus, descended into chaos with the Republican US president interrupting both Biden and the moderator throughout.

“I'm not going to waste my time on a virtual debate, that's not what debating is all about,” Trump said on a phone interview with Fox Business after the nonpartisan commission in charge of presidential debates announced the new format on Thursday morning.

“You sit behind a computer and do a debate — it's ridiculous and then they cut you off whenever they want,” said Trump, who added that he was eager to hold campaign rallies with his supporters.

His decision to forego the debate is the latest whiplash development in the presidential race ahead of the November election. Biden leads in nationwide opinion polls but they show a tighter race in many of the battleground states that may decide the election.

Their two running mates, Vice President Mike Pence and Democratic vice presidential nominee Senator Kamala Harris, engaged in a debate on Wednesday evening.

Biden told reporters on Thursday he would follow the recommendations of the debate commission. Biden said he did not know what action he would take if Trump refused to take part.

“We don't know what the president's going to do. He changes his mind every second,” Biden added.

Even before becoming infected, Trump had faced criticism for his administration's response to a pandemic that has killed more than 210,000 Americans — more than any other country — and thrown millions of people out of work.

Trump's disclosure last Friday that he had tested positive brought the crisis back to the centre of the race. The 74-year-old president spent three days in a hospital in Maryland receiving multiple different types of treatment.

More than six million Americans have already cast ballots ahead of November 3's formal Election Day.

The Commission on Presidential Debates said on Thursday it planned to host a town hall-style conversation and that voters and the moderator would ask the candidates questions from the original debate site in Miami. The debate was planned as the second of three between Trump and Biden, with the third set for October 22.

Both campaigns said they were not consulted on the move, but a Biden aide said the Democratic nominee was still prepared to take part.

“Vice President Biden looks forward to speaking directly to the American people and comparing his plan for bringing the country together and building back better with Donald Trump's failed leadership on the coronavirus that has thrown the strong economy he inherited into the worst downturn since the Great Depression,” Deputy Campaign Manager Kate Bedingfield said.

Ready for rallies

Saying he was feeling “really good,” Trump said he was ready to resume campaign rallies. Such rallies, particularly held indoors, have raised concern among public health exerts about spreading the virus.

Trump returned to the White House from the hospital on Monday. Trump said he is still taking steroids to treat the respiratory disease.

Trump said he did not believe he was still contagious, though that contention was not yet backed up by solid evidence from his doctors.

Centre for Disease Control guidelines say people who are severely ill with Covid-19 might need to stay home for up to 20 days after symptoms first appear. The White House has not provided detailed information on the severity of Trump's illness and has refused to say when he last tested negative for the virus. As a result, it is unclear how long he has been positive.

His campaign manager Bill Stepien, who has also tested positive for the virus, said in a statement the virtual format was not necessary and said Trump would have “posted multiple negative tests” by the time of the debate.

“We'll pass on this sad excuse to bail out Joe Biden and do a rally instead,” said Stepien, without providing details of the rally location or how the campaign would ensure there was no risk of transmitting the virus.

White House economic adviser Larry Kudlow, however, told Fox News later on Thursday that he expected the commission's decision to be revisited and that Trump should appear at the next debate to press his case to the American people.

“I expect you're going to see a renegotiation of that,” he said.

Pence and Harris in their debate clashed over the Trump administration's response to the pandemic.

Biden and Harris will travel together to the battleground state of Arizona on Thursday, while Pence will also visit the state after starting his day in Nevada.

Pence, in the debate on Wednesday, defended Trump's record on the pandemic and other issues under sharp attack by Harris, who said Trump's failures had cost American lives. The mostly civil debate was a sharp contrast to the combative encounter between Trump and Biden.

Trump weighed in on the debate during his call with Fox Business, claiming Pence “destroyed” Harris and twice referring to the US senator as a “monster". The comments reignited criticism of the president for what Democrats say are previous sexist and racist attacks against Harris, the first Black woman to appear on a major party's presidential ticket.