A Democratic mega-donor has put up huge digital billboards calling for the impeachment of Donald Trump in Times Square.

The signs, funded by Tom Steyer, will be displayed in the heart of New York City for ten minutes out of every hour until New Year's Eve.

Mr Steyer has said he will spend $20m on the billboards and television ads asking the public to sign a petition urging Congress to impeach the President.

Tom Steyer stands in front of one of the billboards he has funded in Times Square calling for the impeachment of President Donald Trump (Spencer Platt/Getty Images)

“We’re putting a couple of large billboards in Times Square calling for the impeachment of the president,” the billionaire told Bloomberg Politics.

“We legitimately feel that this is the huge issue in front of the American people that no one is standing up for what the overwhelming number of Americans think.”

The billboards will also show many people have signed the petition to impeach Mr Trump.

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Mr Steyer's national campaign warned Mr Trump had brought Americans "to the brink of nuclear war, obstructed justice at the FBI" and had"taken money from foreign governments and threatened to shut down news organisations," in violation of the US constitution.

“People in Congress and his own administration know this president is a clear and present danger who is mentally unstable and armed with nuclear weapons. And they do nothing,” he added.

“Join us and tell your Member of Congress that they have a moral responsibility to stop doing what’s political and start doing what’s right."

Responding to the ad, Mr Trump tweeted: "Wacky and totally unhinged Tom Steyer, who has been fighting me and my Make America Great Again agenda from beginning, never wins elections!"

Six Democrats in the House of Representatives have recently introduced articles of impeachment targeting Mr Trump.