"The people who knew me then know that this did not happen, and have said so," the conservative judge said in a statement sent to AFP.

The allegation is the latest twist in Kavanaugh's already heated confirmation battle, which is set for a dramatic hearing this week involving a university professor who recently came forward accusing him of assaulting her when they were high schoolers.

The New Yorker article was co-written by Ronan Farrow, whose reportage around disgraced movie mogul Harvey Weinstein was key in opening the floodgates of the #MeToo movement, along with another reporter Jane Mayer.

At least four Democratic senators have received information about Ramirez's allegation, the magazine said, of whom at least two have begun investigating it.

Senior Republican staffers have likewise learned of the allegation and expressed concern about its impact on the nomination, The New Yorker added.

"This is another serious, credible, and disturbing allegation against Brett Kavanaugh. It should be fully investigated," Senator Mazie Hirono, of Hawaii, was quoted as saying.

When The New Yorker first contacted Ramirez, it said she was reluctant to come forward, partly because of gaps in her memory because she had been drinking at the time of the incident.

But having spent six days assessing her memories and consulting with her attorney, she felt more confident and is now calling for an FBI investigation. "I would think an FBI investigation would be warranted," she told The New Yorker.

The magazine said it had not found eyewitnesses to confirm that Kavanaugh was at the party, though one former classmate remembered hearing about the incident from another, and independently corroborated many of the details offered by Ramirez. (AFP)