Elon Musk, the billionaire new owner of Twitter, on Monday called for US voters to back Republican candidates on the eve of knife-edge midterm elections.

"Shared power curbs the worst excesses of both parties, therefore I recommend voting for a Republican Congress, given that the Presidency is Democratic," Musk tweeted to his 114 million followers.

"Hardcore Democrats or Republicans never vote for the other side, so independent voters are the ones who actually decide who's in charge!"

The Tesla boss's stewardship of Twitter – one of the world's leading platforms for discourse and activism – has prompted warnings over its political neutrality.

Musk has indicated he plans to lift the ban on former president Donald Trump, though not before the midterm vote on Tuesday.

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Trump was banned for allegedly inciting last year's attack on the Capitol by a violent mob seeking to overturn the results of the 2020 presidential election.

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Musk's sacking of many Twitter staff has also underlined fears that the site will be flooded by hate speech and disinformation, leading some advertisers to back away.