Michael Moore has warned Hillary Clinton's supporters that early celebrations could hand Donald Trump a victory in the US presidential race as he unveiled a surprise film about the election.

The filmmaker said that a shock win for Trump was still on the cards, despite the Republican's ratings being severely dented in recent weeks following a slew of allegations of sexual harassment against women.

He urged Clinton's supporters not to get complacent as he introduced his new work, Michael Moore In TrumpLand, at an event in New York on Tuesday.

"There's a long tradition of Americans electing people who you don't think that they're going to elect," he told the audience.

Moore, who supports Clinton, also revealed that it was being in the UK around the time of the vote for Brexit that inspired him to rush out the documentary ahead of the presidential vote on November 8.

He described the British vote as a moment when "the disaffected and the abused decided to strike back", adding that the atmosphere felt very similar to pro-Trump strongholds such as Ohio.

Moore's new film is based around a short one-man show about the presidential race which he created and performed earlier this month in Ohio, according to US media.

In it, he urges voters to back Clinton.

The film will screen for one week at the IFC Centre in Manhattan beginning on Wednesday and will also be shown at a cinema in Encino, California, The Hollywood Reporter said.

Moore said he hopes more cinemas will be announced soon.