Donald Trump and Elon Musk's unlikely political marriage exploded in a fiery public divorce Thursday, with the US president threatening to strip the billionaire of his huge government contracts in revenge.

Trump said in a televised Oval Office diatribe that he was "very disappointed" after his former aide and top donor criticized his "big, beautiful" spending bill before Congress.

The pair then hurled insults at each other on social media — with Musk even posting, without proof, that Trump was referenced in government documents on disgraced financier and sex offender Jeffrey Epstein.

The row could have major political and economic fallout, as shares in Musk's Tesla car company plunged and the South African-born tech tycoon vowed that he would end a critical US spaceship program.

Speculation had long swirled that a relationship between the world's richest person and its most powerful could not last long -- but the speed of the meltdown took Washington by surprise.

"I'm very disappointed in Elon. I've helped Elon a lot," Trump told reporters in the Oval Office as visiting German Chancellor Friedrich Merz looked on silently.

"Elon and I had a great relationship. I don't know if we will anymore."

A hurt-sounding Trump, 78, noted in a 10-minute diatribe that it had been only a week since he hosted a grand farewell for Musk as he left the cost-cutting Department of Government Efficiency (DOGE).

Trump later called Musk "crazy" and insisted he had asked the tycoon to leave because he was "wearing thin."

'Ingratitude'

Musk hit back in real time on his X social media platform, saying the Republican would not have won the 2024 election without him and slamming Trump for "ingratitude."

As the spat got increasingly vindictive, Musk also posted that Trump "is in the Epstein files," referring to US government documents on Epstein, whose 2019 jail cell suicide, while awaiting trial, sparked a major conspiracy theory.

"Have a nice day, DJT!" added Musk. 

White House Press Secretary Karoline Leavitt told AFP that Musk's Epstein tweet "is an unfortunate episode from Elon, who is unhappy with the 'One Big Beautiful Bill' because it does not include the policies he wanted."

Musk, who was Trump's biggest campaign donor to the tune of $300 million, separately claimed the Republican would not have won the 2024 election without his support and accused him of "such ingratitude."

He replied "yes" to a post suggesting Trump should be impeached, and blasted Trump's global tariffs for risking a recession.

Trump finally suggested hitting the "crazy" entrepreneur where it hurts, threatening Musk's multibillion-dollar government contracts including for launching rockets and for the use of the Starlink satellite service.

"The easiest way to save money in our Budget, Billions and Billions of Dollars, is to terminate Elon's Governmental Subsidies and Contracts," Trump said on Truth Social.

Again Musk fired back, with the SpaceX chief saying he would begin "decommissioning" his company's Dragon spacecraft -- vital for ferrying NASA astronauts to and from the International Space Station -- in response.

He later appeared to walk that back, replying to a user on Twitter: "OK, we won't decommission Dragon," though his tone was unclear. 

'Abomination'

When the crossfire finally relented after several astonishing hours, Tesla had seen more than $100 billion wiped off the company's value.

Trump and Musk's whirlwind relationship had initially blossomed, with the president backing DOGE's cost-cutting rampage through the US government and the tycoon sleeping over at the White House and traveling on Air Force One.

But the 53-year-old ultimately lasted just four months on the job, becoming increasingly disillusioned with the slow pace of change and clashing with some of Trump's cabinet members.

The two men had however kept tensions over Trump's tax and spending mega-bill relatively civil -- until Musk described the plan, the centerpiece of Trump's domestic policy agenda for his second term, as an "abomination" because he says it will increase the US deficit.

Washington will now intently watch the fallout from the row.

Musk posted a poll on whether he should form a new political party -- a seismic threat from a man who has signaled he is ready to use his wealth to unseat Republican lawmakers who disagree with him.