US President Donald Trump has again raised hopes that a coronavirus vaccine could be three or four weeks away, despite cautionary notes sounded by some US public health officials about such an accelerated timeline.

Speaking at an ABC News-hosted town hall event in Philadelphia on Tuesday (local time), Mr 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.”

Mr Trump’s optimism contrasts with more conservative estimates by drug industry executives or other government officials, including National Institute of Allergy and Infectious Diseases Director Anthony Fauci. He has said to expect a vaccine approval closer to the end of the year with broad distribution next year.

“It is conceivable that you can have it by October, though I don’t think that that’s likely,” Mr Fauci said.

Mr 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.

Mr Trump mounted a broad defence of his response to the pandemic, which has killed more than 196,000 Americans since February, again insisting that the virus “is going to go away.”

“It would go away without the vaccine,” he told the host.

“You’ll develop like a herd mentality, it’s going to be herd developed, and that’s going to happen. That will all happen.”

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

Mr 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.

-with agencies