The district attorney of Philadelphia said on Monday that he has filed a lawsuit to halt Elon Musk's US$1 million giveaways as part of his political organisation's effort boosting Donald Trump's presidential campaign.

The suit by Democratic District Attorney Larry Krasner is the first legal action to be brought over the sweepstakes offering US$1 million every day until November 5 to a person in a battleground state who has signed a petition supporting the Constitution.

Krasner's office said the lawsuit, coming just over a week before Election Day, doesn't preclude potential criminal action.

“The Philadelphia District Attorney is charged with protecting the public from public nuisances and unfair trade practices, including illegal lotteries. The DA is also charged with protecting the public from interference with the integrity of elections,” Krasner's office said in a statement published on its website.

A spokesperson for the billionaire tech mogul's America PAC (political action committee), emailed for comment on the lawsuit and asked if the cash awards would continue, responded with a link to an X post, which showed the latest US$1 million winner holding an oversized check.

Speaking in Delaware after casting his ballot Monday, US President Joe Biden called the giveaway “totally inappropriate.”

Musk's giveaway requires entrants to sign a petition backing the First and Second Amendments of the Constitution and calls for them to serve as spokespeople for the organization as a condition of winning.

The awards have carried on after election law experts raised questions that it violates federal law barring anyone from paying a person to vote or register to vote.

In his statement announcing the lawsuit, Krasner characterised the US$1 million prize as a “lottery,” which would make it more heavily regulated than if it were a prize or work-related. (AP)