Joe Biden said that while he trusts what scientists say about a potential coronavirus vaccine, he doesn't trust US President Donald Trump.

His comments come as the debate over a vaccine how it will be evaluated and distributed when it's ready has taken centre stage in the presidential race with seven weeks to go until the November election.

Trump and Biden have been trading accusations that the other is undermining public trust in a potential coronavirus vaccine. Biden has expressed concerns that the vaccine approval process could be politicized, while Trump and his allies counter that such comments from Biden and other Democrats are turning off the public to a potentially lifesaving vaccine when it's released.

Biden, speaking in Wilmington, Delaware, after being briefed by public health experts about a potential vaccine, cited Trump's incompetence and dishonesty surrounding the distribution of personal protective equipment and coronavirus testing.

The US can't afford to repeat those fiascos when it comes to a vaccine," he said.

I trust vaccines, I trust scientists, but I don't trust Donald Trump," Biden said, "and at this moment, the American people can't, either.

On Wednesday evening, Trump raised new questions about the administration's rollout of a vaccine when he publicly contradicted the director of the Centers for Disease Control and Prevention, who said at a congressional hearing earlier Wednesday that a vaccine wouldn't be broadly available to most Americans until the summer of 2021.

Trump said that CDC Director Robert Redfield had misspoken and that the U.S. could start distributing a vaccine starting in mid-October.

I think he made a mistake when he said that. I think it's just incorrect information, Trump said of Redfield's comments. When he said it, I believe he was confused. He said he called Redfield after his testimony. I think he just made a mistake. He just made a mistake. I think he misunderstood the question, probably.

For his part, Biden has said he would take a vaccine tomorrow if it were available but that he would want to see what the scientists said first.

His running mate, Kamala Harris, has said she wouldn't trust Trump to be honest about the safety of any potential vaccine and worries that experts and scientists would be muzzled by the president because he's so eager to get a vaccine approved by his stated goal of Election Day.