Celebrities such as Robert De Niro, Alec Baldwin and Michael Moore have joined thousands of people outside Donald Trump's signature New York building to speak out against the incoming US president.

The event, staged on the eve of his inauguration in front of Trump International Hotel and Tower, was a rally for city residents who have vowed to go their own way on healthcare, climate change and other issues during the next four years.

Documentary maker Moore, who helped organise the event, told the crowd on Thursday: "As bad we think it's going to be, it's going to be worse. But the good news is there's more of us than there are of them."

He urged people to regularly call their representatives in Congress to make their views known.

Baldwin, who portrays Trump on NBC's Saturday Night Live, said Americans wary of Trump's policies should become more involved.

He briefly did his Trump impression, which has drawn barbs from the president- elect.

Other celerities at the event included actors Sally Field, Mark Ruffalo, Marisa Tomei, Julianne Moore and Cher.

Minneapolis mayor Betsy Hodges joined New York mayor Bill de Blasio at the protest, with Democrat de Blasio making a point of defying potential Trump policies.

"Donald Trump may control Washington, but we control our destiny as Americans," de Blasio said.

"We don't fear the future. We think the future is bright, if the people's voices are heard."

But a Quinnipiac University poll shows New Yorkers are split on how de Blasio should deal with the Trump White House.

Forty-six per cent say de Blasio should try to get along with Trump, while 45 per cent say de Blasio should be a national leader in opposing Trump's policies.

Trump, a New York real estate mogul, was in Washington DC, where he is scheduled to be sworn in on Friday as the 45th president.

Protests are expected to continue on inauguration day, with the number of planned rallies far above what has been typical at recent presidential inaugurations.

About 30 permits have been granted in Washington for anti-Trump rallies, and sympathy protests are planned in cities from Boston to Los Angeles as well as outside the US in places such as London and Sydney.