White House chief of staff John Kelly will leave his post at the end of the year, US President Donald Trump has confirmed.

Kelly's successor should be announced in the coming day or two, Trump has told reporters in Washington on Saturday.

US media outlets have pegged Vice President Mike Pence's 36-year-old chief of staff Nick Ayers as a likely candidate to take Kelly's place.

Speculation that Kelly would resign has been rife in recent days, with media outlets citing a deterioration in the relationship between the president and his chief.

"John Kelly will be leaving - I don't know if I can say 'retiring'. But, he's a great guy," Trump said as he made the announcement.

Former homeland security secretary Kelly was tasked with bringing order to the White House when he took over from Reince Priebus in July 2017.

In September, veteran Washington Post reporter Bob Woodward quoted Kelly as calling Trump "an idiot".

"It's pointless to try to convince him of anything. He's gone off the rails. We're in Crazytown. I don't even know why any of us are here. This is the worst job I've ever had," Kelly was quoted as saying in Woodward's book on the Trump White House.

Kelly denied he had made the comments at the time, but rumours persisted that the relationship between the two was suffering.

Kelly's exit marks the latest in a long list of advisers and cabinet members to come and go from the White House under Trump.

It is the second top-level personnel change Trump has made since the mid-term elections on November 6, after Attorney General Jeff Sessions resigned last month at Trump's request.