Speaking at an ABC News-hosted town hall in Philadelphia on Tuesday, Trump defended his handling of the pandemic and said a vaccine could be ready for distribution before the November 3 presidential election.

"We're very close to having a vaccine," he said.

"If you want to know the truth, the previous administration would have taken perhaps years to have a vaccine because of the FDA and all the approvals. And we're within weeks of getting it...

"Could be three weeks, four weeks."

Earlier this month, top US infectious disease expert Dr Anthony Fauci told CNN most experts believe a vaccine will be ready by November or December.

"It is conceivable that you can have it by October, though I don't think that that's likely," he said.

Trump bristled at tough questions from uncommitted voters and ABC News host George Stephanopoulos during the town hall meeting, arguing that his decision to impose travel bans on China and Europe had saved thousands, if not millions, of lives.

The United States has reported nearly 6.6 million cases of COVID-19, the disease caused by the virus, the highest number worldwide, and nearly 195,000 deaths.

Trump repeated a claim he made early on in the pandemic that the virus would disappear on its own and denied understating the threat of the disease.

Australian Associated Press