Joe Biden said on Friday he's ready to face off against his White House challenger Donald Trump in a debate ahead of their likely presidential rematch in November.

Candidate debates have been important milestones in US presidential elections for decades, helping make or break voters' opinions of the contestants' personal style and demeanor as much as their policy chops.

But Biden's team has for months been non-committal about his willingness to participate in the tradition, which is usually held in front of an audience and moderated by a well-known journalist.

"I am happy to debate him," Biden told radio host Howard Stern Friday.

"I am, somewhere. I don't know when," he said.

"Ok, let's set it up!" Trump campaign advisor Chis LaCivita said on X, formerly Twitter, in response to Biden's comments.

Presumptive Republican nominee Trump declined to face off against his primary opponents in any debates during the 2024 cycle.

But he has indicated his eagerness with the man who beat him in 2020, saying on social media earlier this year that he was ready to hold a presidential debate with Biden "ANYTIME, ANYWHERE, ANYPLACE!"

Biden, who has branded Trump as a threat to democracy, told reporters last month that any agreement to debate the real estate mogul "depends on his behaviour."

The nonpartisan Commission on Presidential Debates (CPD) has already arranged three dates and locations for Trump and Biden to go head-to-head for the 2024 fight, at US universities throughout the country in September and October.

But Trump bashed the CPD as being biased toward Democrat Biden when in 2020 it planned to move a third and final debate to a virtual format amid the Covid-19 pandemic.

Then-president Trump had himself shown up to the second 2020 debate against Biden only three days before testing positive for Covid.

Biden at the time had said he would not participate in another in-person debate with Trump while the Republican was still ill.

A verbal spar could be a useful opportunity for both the 77-year-old former president and 81-year-old current president to display stamina, as Biden is still dogged by Trump's old "Sleepy Joe" nickname -- and Trump faced online teasing when he appeared to nod off during his criminal trial in New York last week. (AFP)