Scarlett Johansson has joined forces with Julianne Moore, Robert Downey JR, and more to stand up against Donald Trump, in a video that is fast gaining traction online.

The projectwas the brainchild of Buffy the Vampire Slayer writer and director Joss Whedon, who shared it after a 19-month hiatus from social media.

Troubled by growing support for Donald Trump in the US Presidential Campaign, Whedon returned to Twitter on Wednesday to launch his star-studded Save The Day video.

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In the clip, we see A-listers - including the likes of Firefly's Nathan Fillion, Mark Ruffalo, Don Cheadle, Martin Sheen, Yvette Nicole Brown, and more – as they pretend to fight for our attention.

Sure, it’s funny - but, at the heart of it all, these celebs are promoting an important message: they want the American people to register to vote on 8 November.

Speaking together, they explain: “The issue is one that truly matters to all of us. Such as a disease, or an ecological crisis, or a racist abusive coward who could permanently damage the fabric of our society.

“Do we really want to give nuclear weapons to a man whose signature move is firing things?”

They continue, some of them tearfully: “But we can end this nightmare before it begins – we can save the day for our children, for our communities, for America.

“All it takes is all of us... we can’t say one vote doesn’t matter – your vote matters.

"It affects everything; not just the presidency, but the senate, the house, immigration, student debt, common sense gun laws, the supreme court.”

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They finish: “This isn’t just an election, it’s a tipping point for the country, for the world, for your world.”

Whedon has since revealed that he had no trouble finding stars to appear in the video.

The self-proclaimed feminist told Buzzfeed: “There is almost nobody that I wouldn’t approach to say, ‘If you can pitch in, do it now.

“It was pretty much the same spiel to everybody: ‘Doing a voting PSA to help get out the vote and stop orange Muppet Hitler.’”

Rumour has it that this is the first of many videos to come, with Whedon joking that he has yet to save democracy.

The link points to website savetheday.vote, which reads: “We are a short-form production company dedicated to the idea that voting is a necessary and heroic act. That every voice in this wonderfully diverse nation should, and must, be heard. That the only thing that can save democracy is the act that defines it.

“We are committed to fighting the apathy, cynicism, and honest confusion that keeps citizens from using their vote. And to reminding an increasingly out-of-touch and compromised set of representatives that they are answerable to the people they were hired to serve.”