Top US virus expert Dr Anthony Fauci has criticised the White House for hosting a gathering last month that has been linked to an outbreak of Covid-19. 

The event at the White House on Saturday 26 September, for the president's nomination of Amy Coney Barrett as a Supreme Court justice, is thought to be the root of the localised outbreak.

Dr Fauci, a member of the White House coronavirus task force, said the gathering was a "superspreader event".

More than 30 people are thought to have been infected at the White House ceremony including the president himself.

Trump has been talking up an experimental Covid-19 treatment he received as "a cure," but Fauci, who gave an interview to CBS News on Friday, said referring to it as such may cause "confusion."

Asked about Trump's effusive praise for Regeneron's antibody treatment, Fauci said that talking about a "cure" could be misleading because it hasn't yet been proven, and the drugs that are currently available have only been shown to have modest to moderate results.

"We don't have any indication -- I think you really have to depend on what you mean by a cure, because that's the word that leads to a lot of confusion," he said.

He warned everyone against coming to a conclusion without scientific evidence.

Fauci was also asked about the low level of mask use at the White House until recently, and what lessons could be learned.

"I think the — the data speaks for themselves," the scientist said of mask-wearing.  "We had a super-spreader event in the White House and it was in a situation where people were crowded together and were not wearing masks. So the data speak for themselves."

Fauci said he had faith that the president's medical team wouldn't allow him to o out campaigning while he is still contagious.

"I can tell you, they are going to be testing him to determine the trajectory and whether he gets to the point where he's not infected," he said. "I can guarantee you that they will be testing him before they let him go out."