US President Donald Trump praised billionaire Elon Musk's efforts to cut federal spending during a joint press conference in the Oval Office on Friday, as the Tesla CEO departs the administration after a chaotic tenure that saw the elimination of thousands of jobs and billions of dollars in contracts.

Musk, who headed the Department of Government Efficiency, disrupted numerous agencies across the federal bureaucracy but ultimately fell far short of the massive savings he had initially promised.

"Elon has worked tirelessly helping lead the most sweeping and consequential government reform program in generations," Trump said from behind the Resolute Desk, as Musk stood to his right, wearing a black Doge hat and a t-shirt that read "The Dogefather" in the style of the movie "The Godfather."

In recent days, Musk had prompted some frustration among White House officials by criticising Trump's sweeping tax and spending bill as too expensive.

There was no evidence of tension during the joint appearance on Friday, where Trump said Musk would continue to play a role in his administration.

"Elon is really not leaving," Trump said. "He's going to be back and forth."

Initially, the White House and senior aides insisted Musk, the world's richest man, was a key figure who wasn't going anywhere.

But more recently, they began pointing to the expiration of his 130-day mandate as a special government employee, which was set to end around May 30, as a natural endpoint.

Musk has said he intends to devote most of his energy to his business empire, including Tesla and SpaceX, after some investors expressed concern that Doge was occupying too much of his time.

He has also said he plans to ratchet back his political spending, after he spent nearly US$300 million backing Trump's presidential campaign and those of other Republicans in 2024.

Musk initially claimed Doge would slash at least US$2 trillion in federal spending. Four months into its efforts, Doge now estimates it has saved US$175 billion.

But the details it has posted on its website, where it gives the only public accounting of those changes, add up to less than half of that figure.

Musk said on Friday that he would continue to serve as a Trump adviser and expressed confidence that Doge would eventually achieve much deeper savings.

"This is not the end of Doge but really the beginning," he said. (Reuters)