Biden and Trump set for live TV debate

US President Joe Biden and former president Donald Trump will meet on a debate stage on Thursday for the first of two televised face-offs that could prove critical in their rematch race to win the White House in November.

More than four months ahead of the November 5 vote, the CNN debate will be the earliest presidential debate in modern US history.

Broadcaster CNN said only Biden and Trump met its conditions for participating in the debate: appear on enough state ballots to potentially win the presidency and receive at least 15 per cent in four separate national polls of registered or likely voters.

Independent presidential candidate Robert F. Kennedy Jr did not make the cut.

In Thursday's 90-minute debate, candidates will appear at a uniform podium, be given a pen, paper and bottle of water and cannot use props or notes, CNN said.

Biden will be on the podium on the right side of viewers' screens, and Trump will get the last word after a coin toss.

Campaign staff may not interact with candidates during the two commercial breaks, and there will be no studio audience.

US presidential debates often draw tens of millions of viewers, and through history have determined the course of some races. This time, strategists say there are risks for both candidates, who are locked in a tight race and share low enthusiasm from voters.

Biden, 81, and former president Trump, 78, are the oldest candidates ever to seek the presidency and viewers are sure to question their cognitive abilities and emotional steadiness.

Trump aides see Biden as prone to verbal slip-ups that could amplify voter concerns about the president's age.

Trump's role in the January 6, 2021, attack on the US Capitol, efforts to overturn the 2020 election and his conviction on 34 felony counts for involvement in a hush money scheme could come up during the debate, as could the legal woes facing Biden's son, Hunter, who was convicted of lying about his drug use to illegally buy a gun.

According to Nielsen Media Research, more than 73 million people tuned in for the first Biden-Trump debate in 2020.