Elon Musk warned Thursday that the "fate of Western civilization" depends on Donald Trump returning to office as the tech billionaire launched five nights of campaign events for the White House candidate in the key swing state of Pennsylvania.

The Tesla and SpaceX CEO has emerged as a major voice in U.S. politics but is accused of turning the social media platform X into a megaphone for right-wing conspiracy theories since acquiring it in 2022.

"I can't emphasize enough that Pennsylvania is, I think, the lynchpin in this election," he said at a town hall event in Folsom, on the outskirts of Philadelphia. "And this election, I think, is going to decide the fate of America and, along with the fate of America, the fate of Western civilization."

Musk, the world's richest man, announced that his events would be free to attend for anyone who had voted early in the presidential election and signed a petition "supporting free speech & right to bear arms."

Trump is in a knife-edge election against Democratic Vice President Kamala Harris, less than three weeks ahead of Election Day.

Musk, who endorsed Trump in July, is one of the Biden administration's fiercest critics and frequently spreads far-right misinformation about undocumented immigrants and voter fraud.

Describing himself as "pro-immigrant", Musk spent much of his opening night in Pennsylvania complaining about crime and border security, saying the southern frontier "looks like World War Z, okay -- it's like zombie apocalypse."

Republicans have complained for years about anti-conservative bias on social media, often citing Trump's 2021 suspensions and pre-Musk X -- then known as Twitter -- blocking users from linking to a newspaper article critical of Joe Biden's son.

Musk, though, has taken an increasingly visible role in Trump's campaign, accompanying him on stage at a recent rally in Pennsylvania and frequently lambasting Harris.

The billionaire has donated almost $75 million to his political organization America PAC, set up to help Trump back into office, and has promised residents in swing states $47 for each registered voter who signs his petition.

Trump has made a point of praising the 53-year-old during multiple campaign events this week, after tapping the tycoon to run a committee tasked with slashing government bureaucracy and waste if the Republican nominee wins the election.

Trump has largely handed off his grassroots "get-out-the-vote" push to Musk's America PAC in Pennsylvania and the other swing states expected to determine the election.

Rolling Stone reported this week that Republicans have voiced fears that the organization is making a mess of the job, with a relatively small presence on the ground despite its massive spending.