A new video featuring "a sh*t tonne of famous people" has aired calling Donald Trump a "racist, abusive coward" and telling people to get out and vote against him.

Celebrities including Scarlett Johansson, Robert Downey Jr, Julianne Moore, Leslie Odom Jr, James Franco and Mark Ruffalo feature in the ad encouraging people to register to vote, with a not-so- subtle suggestion the vote should be for Hillary Clinton.

"On Tuesday November 8 this county will make one of the most important decisions in its history," the celebrities in the advert state.

"You have a chance, you have an obligation, to be part of that decision. You might think it's not important, you might think you're not important – but that's not true and the only way we can prove that to you is by having lots of famous people, just a sh*t tonne of famous people repeating how important it is. Register. Vote," the ad explains.

"You only get this many famous people together if the issue is one that truly matters to all of us – a disease or ecological crisis or a racist, abusive coward who could permanently damage the fabric of our society.

"Do the math; do we really want to give nuclear weapons to a man whose signature move is firing things?"

The video, from the Save the Day PAC, tells people they must register in order to have a say in the upcoming election – and despite not being endorsed by a candidate, the campaign is no fan of the GOP candidate.

In addition to making a few digs at The Donald's expense, the ad also suggests actor Mark Ruffalo will get naked if people visit the savetheday.vote website and register.

"If you do vote and help protect this country from fear and ignorance Mark Rufalo will do a nude scene in his next movie... Mark's going to get his d*ck out. Full Monty. Full Marky," the video states. "Make Mark be naked, by making your mark on November 8."