Philadelphia, Pennsylvania - Elon Musk is expected in court in Philadelphia on Thursday, after a judge ordered him to attend a hearing in a lawsuit seeking to halt his $1 million giveaways to registered US voters in swing states.

Philadelphia's chief prosecutor Larry Krasner lodged the suit on Monday, calling Musk's project "an illegal lottery scheme", with the judge in the case ruling Wednesday that the billionaire is required to appear in court.

"It is further ordered that all parties must be present at the time of the hearing," judge Anne Marie Coyle said.

The far-right billionaire announced the daily contest this month, prompting the Justice Department to warn that it may violate federal law, which prohibits paying people to register to vote.

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Musk has thrown his millions, time, and considerable influence into backing Republican presidential candidate Donald Trump since endorsing him in July.

The world's richest man has reportedly donated $118 million to his personal pro-Trump political action committee, an organization which collects funds for elections.

He has also appeared on stage with Trump at a campaign rally in Pennsylvania and hosted a series of town halls on his own in a battleground state critical in the November election.

Musk previously supported Barack Obama but has become a major far-right figure in recent years, spreading racist and antisemitic conspiracy theories on X, the platform he owns.