US President Donald Trump said on Friday that Elon Musk had "lost his mind" but insisted he wanted to move on from the fiery split with his billionaire former ally.

The blistering public break-up between the world's richest person and the world's most powerful is fraught with political and economic risks all round.

Trump had scrapped the idea of a call with Musk and was even thinking of ditching the red Tesla he bought at the height of their bromance, White House officials told AFP.

"Honestly I've been so busy working on China, working on Russia, working on Iran... I'm not thinking about Elon Musk, I just wish him well," Trump told reporters aboard Air Force One en route to his New Jersey golf club late on Friday.

Earlier, Trump told US broadcasters that he now wanted to focus instead on passing his "big, beautiful" mega-bill before Congress – Musk's harsh criticism of which had sparked their break-up.

But the 78-year-old Republican could not stop himself from taking aim at his South African-born friend-turned-enemy.

"You mean the man who has lost his mind?" Trump said in a call with ABC when asked about Musk, adding that he was "not particularly" interested in talking to the tycoon.

Trump later told Fox News that Musk had "lost it."

Just a week ago Trump gave Musk a glowing send-off as he left his cost-cutting role at the so-called Department of Government Efficiency (Doge) after four months working there.

While there had been reports of tensions, the sheer speed at which their relationship imploded stunned Washington.

After Musk called Trump's spending bill an "abomination" on Tuesday, Trump hit back in an Oval Office diatribe on Thursday in which he said he was "very disappointed" by the entrepreneur.

The row then went nuclear, with Musk slinging insults at Trump and accusing him without evidence of being in government files on disgraced financier and sex offender Jeffrey Epstein.

Trump hit back with the power of the US government behind him, saying he could cancel the Space X boss's multi-billion-dollar rocket and satellite contracts.

Trump struck a milder tone late Friday when asked how seriously he is considering cutting Musk's contracts.

"It's a lot of money, it's a lot of subsidy, so we'll take a look – only if it's fair. Only if it's to be fair for him and the country," he said.

Musk apparently also tried to de-escalate social media hostilities.

The right-wing tech baron rowed back on a threat to scrap his company's Dragon spacecraft – vital for ferrying Nasa astronauts to and from the International Space Station.

And on Friday the usually garrulous poster kept a low social media profile on his X social network.

However, the White House denied reports that they would talk. (AFP)