Washington DC - President Joe Biden launched a scorching attack on his "dangerous" election rival Donald Trump in Thursday's State of the Union address, delivering a barnstorming performance to make his case for four more years.

Biden (81) let the punches fly from the opening moments, accusing the Republican of "bowing down" to Russian President Vladimir Putin and lashing him on everything from abortion to the economy.

"Not since President Lincoln and the Civil War, have freedom and democracy been under assault at home as they are today," he said. "What makes our moment rare is that freedom and democracy are under attack at both at home and overseas."

In one of the most direct attacks in memory by a president on an election challenger during the State of the Union, Biden never said Trump's name but instead blasted him 13 times as merely "my predecessor."

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Trump's recent comments calling the US commitment to NATO into doubt were "bowing down to a Russian leader" he said, before vowing to cheers from Democrats: "I will not bow down."

The annual set-piece presidential speech was a unique chance for Biden to pitch his reelection message in front of his closest political allies and foes – and a national TV audience of millions of voters – ahead of November's election.

At just over an hour long, it was also a high-stakes test of Biden's ability as the oldest ever US president to think – and stay – on his feet.

Republicans frequently booed and heckled Biden, but he shot back each time, sprinkling his delivery with jokes that mocked his opponents.

Democrats feted him with chants of "four more years" and Vice President Kamala Harris repeatedly rose to her feet to applaud Biden from her seat behind him, while Republican House Speaker Mike Johnson shook his head.

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Trump (77) has a narrow lead over Biden in opinion polls. However, he faces multiple criminal charges linked to his efforts to overturn his 2020 election loss and refusal to give back boxes of top-secret documents after grudgingly leaving the White House.

Trump had promised retorts throughout the speech posted on his social media platform, Truth Social, but only offered a lukewarm and glitchy response as the website repeatedly crashed.

"He looks so angry when he's talking, which is a trait of people who know they are 'losing it.' The anger and shouting is not helpful to bringing our Country back together!" Trump posted.

In his speech, Biden slammed Republican abortion opponents, saying they have "no clue about the power of women in America," in what Democrats see as a key vote-winning issue.

And he touted the booming US economy as the "greatest comeback story never told," even if Americans are still unhappy with high prices and polls show many saying their economic fortunes have not improved.

"I inherited an economy that was on the brink," he said. "Now our economy is literally the envy of the world."

Biden took on the war on Gaza, which has provoked fury among many Democrats and the Arab-American community, angered by the president's strong support for Israel's assault and accusing him of complicity in genocide.

He called for an "immediate ceasefire" – meaning a six-week temporary pause – and announced that he has ordered the US military to set up a temporary port on Gaza's coast to bring in aid, while promising "no US boots will be on the ground."

Protesters against his support for Israel had earlier tried to block the presidential motorcade from the White House to Congress. Some progressive members of Congress donned traditional Palestinian keffiyehs and ceasefire pins and held up signs during the address in solidarity with Gazans under siege.

Biden, meanwhile, sought to turn the tables on Republicans on the hot-button issue of migration, calling them out for refusing to pass a bill that would have severely clamped down on the right to seek asylum and further militarized the US-Mexico border.

"We can fight about fixing the border or we can fix it," he said in response to heckling from Republican right-winger Marjorie Taylor Greene.

With polls showing Biden's age is a top concern for voters, Biden also pushed back on the narrative that he is too old to serve.

"I know it may not look like it but I've been around a while," he said to laughter.

But "when you get to be my age certain things become clearer than ever. I know the American story."

In line with tradition, First Lady Jill Biden hosted a number of guests chosen to highlight the White House's priorities.

This year, they include a Texan woman forced to leave the state for an abortion, a woman whose IVF treatment was halted by an Alabama court ruling, and the prime minister of Sweden, which became NATO's newest member on Thursday.