US President Joe Biden took on Donald Trump in a fiery speech to Congress on Thursday, accusing his election rival of threatening US democracy and kowtowing to Russia, as he laid out his case for four more years in the White House.

In his last State of the Union address before the election, Biden, a Democrat, charged Trump, his Republican challenger in the November 5 election, with burying the truth about the January 6, 2021, Capitol assault, bowing to Russian President Vladimir Putin and torpedoing a bill to tighten restrictions at the US border with Mexico.

The 68-minute speech gave Biden, who is suffering from low approval ratings, a chance to speak directly to millions of Americans about his vision for another four-year term and present a contrast with Trump, whose name he did not mention but whose presence reverberated throughout the speech.

Speaking before a joint session of the House of Representatives and the Senate, Biden opened his remarks with direct criticism of Trump for his comments inviting Russian Putin to invade other Nato nations if they did not spend more on defence.

"Now my predecessor, a former Republican president, tells Putin, quote, 'Do whatever you want,'" Biden said.

"I think it's outrageous, it's dangerous and it's unacceptable."

Biden, who has been pushing Congress to provide additional funding to Ukraine for its war with Russia, also had a message for Putin: "We will not walk away," he said.

The president also drew a contrast with Trump over abortion rights and the economy, and he directed several barbs at Republican lawmakers in the chamber with off-the-cuff banter that appeared designed to assuage concerns about his age and mental acuity.

Biden came out swinging at the top of his speech with robust attacks. He accused Trump and Republicans of trying to rewrite history about the January 6, 2021, Capitol riot by the former president's supporters seeking to overturn Biden's 2020 victory.

"My predecessor and some of you here seek to bury the truth about January 6. I will not do that," Biden said, a signal that he will emphasise the issue during his re-election campaign. "You can't love your country only when you win."

Trump, meanwhile, sent a steady stream of messages blasting Biden on his Truth Social platform. "He looks so angry when he’s talking, which is a trait of people who know they are 'losing it,'" Trump wrote. "The anger and shouting is not helpful to bringing our Country back together!"

Opinion polls show Biden, 81, and Trump, 77, closely matched in the race. Most American voters are unenthusiastic about the rematch after Biden defeated Trump four years ago.

Meanwhile, Biden denounced his predecessor as all talk on the rivalry with China as the Democrat highlighted actions to curb exports of high technology.

"Frankly, for all his tough talk on China, it never occurred to my predecessor to do any of that," Biden said.

And he sought to cool anger among many Democrats over his support for Israel's offensive in Gaza following the October 7 Hamas attacks.

He announced that the US military will build a port on Gaza's Mediterranean coast to receive humanitarian assistance by sea.

The president's wife's guests for the speech include Swedish Prime Minister Ulf Kristersson, who was in Washington as Sweden formally joins Nato on Thursday, two years after the start of the war in Ukraine, indicating Biden will speak on his support for the security alliance, another contrast with Trump. (Reuters, with additional reporting by AFP)