A judge has ordered Elon Musk to attend a court hearing in Philadelphia in a lawsuit seeking to stop a political action committee awarding $US1 million to US voters ahead of Tuesday’s presidential election.

The Philadelphia District Attorney’s Office filed the lawsuit on Monday (local time).

It called the giveaway by Musk’s America PAC, which backs Republican former president Donald Trump, an “illegal lottery” that enticed Pennsylvania residents to share personal data.

“It is further ordered that all parties must be present at the time of the hearing,” a judge wrote in an order with the Philadelphia County Court of Common Pleas.

The hearing in the case was moved up to Thursday morning from Friday (local time).

Trump faces Democratic Vice President Kamala Harris in what polls show to be a tight race for the White House.

A representative for America PAC did not immediately respond to a request for comment.

Musk’s representatives have not responded to requests for comment.

Musk promised to give $US1 million ($A1.5 million) each day to someone who signs his online free-speech and gun-rights petition.

Legal experts consulted by Reuters last week were divided on whether the giveaway violated federal laws that make it a crime to pay or offer to pay a person to register to vote.

The Justice Department sent a letter to America PAC warning that the billionaire’s giveaways for registered voters who signed his petition might violate federal law, CNN reported last week.

The Trump campaign is broadly reliant on outside groups for canvassing voters, meaning the super PAC founded by Musk – the world’s richest man – plays an outsized role in what is expected to be a razor-thin election.

-AAP