Washington DC - Donald Trump on Wednesday challenged Joe Biden to an election debate after the two men emerged from primary voting as the all-but-certain Republican and Democratic candidates in November's US presidential vote.

"It is important, for the Good of our Country, that Joe Biden and I Debate Issues that are so vital to America, and the American People," said Trump, who ducked out of every debate in the race for the Republican nomination.

"I am calling for Debates, ANYTIME, ANYWHERE, ANYPLACE!" he wrote on his Truth Social platform.

Trump (77) sewed up the Republican nomination during the 15-state Super Tuesday voting bonanza as he saw off sole remaining challenger, Nikki Haley, in every state except Vermont. Biden will almost certainly be his opponent.

Trump was repeatedly challenged by Haley and his other primary rivals to show up for the Republicans' televised debates, but he refused, reckoning that he had nothing to gain from sharing a spotlight with lower-polling rivals.

But he is polling within the margin of error against 81-year-old Biden and has reversed his position, saying he would even agree to debates hosted by the Democrats.

Biden – who, along with Trump, has faced questions over his age and mental acuity – has not revealed whether he is open to debating Trump.

The pair faced off twice in 2020, but the first match-up descended into chaos as Trump spent much of the time shouting Biden down, and a third debate was canceled following Trump's refusal to conduct it virtually due to Covid-19.

Trump also vowed to conduct a "rapid response" to Biden during his State of the Union address, arguing that it was "important for the country to get the truth."

The annual speech takes place on Thursday, when the president will set out his governing vision, tout his record, and make the case for four more years.

While Biden has been occasionally criticized for distortions of the truth, Trump makes false statements almost every time he speaks in public.

His persistent false claim that fraud was to blame for his 2020 election defeat to Biden features in the criminal indictments he faces and was encapsulated by a phrase that has become part of the political lexicon – "The Big Lie."

The Washington Post cataloged more than 30,000 false or misleading claims made in public by Trump during his first term – around 21 a day.