US President Donald Trump on Monday again hinted a coronavirus vaccine will be available before November's election, as he accused his Democratic rivals for the White House of undermining public confidence in the immunization.

His comments came days after vice presidential nominee Kamala Harris said she would not take Trump's word on the safety and efficacy of an anti-virus vaccine, if one were ready before the US presidential vote.

Trump faces intense pressure to curb the contagion that has clouded his re-election prospects, sparking worries his administration could rush vaccine research to fit a political timetable.

Biden also weighed in on Monday, saying he wanted transparency and scientific facts on any future vaccine.

"I'm worried if we do have a really good vaccine, people are going to be reluctant to take it. So he's (Trump) undermining public confidence," Biden added.

Trump, who is behind in national polls, fired back saying his rivals in the November 3 vote had both delivered "reckless anti-vaccine rhetoric."

"It's so dangerous for our country what they say," Trump told a press conference. "The vaccine will be very safe and very effective."

A shot to protect against the virus that has killed more than 189,000 in the US and hobbled the world's largest economy has become another flashpoint ahead of polling day.

News broke last week that the US Centers for Disease Control and Prevention asked states to sweep away red tape that could prevent a network of vaccine distribution centers being "fully operational by Nov 1, 2020."

The president, after telling journalists to take off their anti-virus facemasks, also suggested again that a vaccine could be available before voters head to the polls.

"We're going to have a vaccine very soon, maybe even before a very special date," Trump said.