US President Joe Biden has received a standing ovation and rapturous applause from a sea of supporters waving “We love Joe” banners as he gave his farewell speech at the Democratic National Convention.

Biden was forced to pause for several minutes as the crowd chanted, cheered and called when he took to the stage in Chicago on Tuesday (AEST).

With a wide grin, Biden was at times also emotional and had tears as he looked around the arena, with the Jackie Wilson song (Your Love Keeps Lifting Me) Higher and Higher energising the delegates.

“America, I love you,” he said in response to the chants of “We love Joe, we love Joe” and “Thank you Joe”.

In his keynote speech, Biden threw his support behind his Vice-President, Kamala Harris, who stood and clapped with everyone else.

“Let me ask you … are you ready to vote for freedom?” he said, as the crowd went wild.

“Are you ready to vote for democracy and for America?

“Let me ask you – are you ready to elect Kamala Harris and Tim Walz?”

At times feisty and slamming Republican challenger Donald Trump as a “loser”, Biden warned of the threat the former president posed now and if he lost the election again.

As Harris prepares to face off against Trump in the fight for the American presidency, Biden warned the country was at an “inflection point”.

“One of the rare moments in history where the decisions we make now will determine the fate of our nation and the world for decades to come,” he said.

“That’s not hyperbole, I mean it literally. We’re in the battle for the very soul of America.”

Jill and Joe Biden make their appearance on stage. Photo: Getty

Warning about the threat Trump posed to democracy, Biden said November’s election would be the first since the January 6 riots on Capitol Hill when “we almost lost everything about who we are as a country”.

“That threat – this is not hyperbole – is still very much alive,” he said.

“Donald Trump says he will refuse to accept the election result if he loses again. Think about that. He means it.

“Think about that. He is promising a bloodbath if he loses, in his words. That he will be a dictator on day one, in his own words. By the way, he means it. I’m not joking.”

In the lengthy address, Biden touted his administration’s accomplishments – boosting the US economy and strengthening US alliances abroad – and condemned the racism and white supremacy that continue to plague America, saying there was no place for them.

Biden said selecting Harris as his Vice President in the 2020 election campaign was the “best decision I made my whole career”.

“We have … become close friends. She is tough, experienced and she has enormous integrity. Her story represents the best American story.

“Like many of our best presidents, she was also Vice President.

“She will be a president our children can look up to. She will be a president respected by world leaders, because she already is.

“A president we can all be proud of. And she will be a historic president who puts a stamp on America’s future.”

Biden told his supporters it had been the honour of his lifetime to serve as president, and it was time to vote.

“I love the job. I love my country more. And all this talk about how I’m angry with all those people who said I should step down – it’s not true,” he said.

“We need to preserve our democracy. In 2024, we need you to vote.

“We need you to keep the Senate.

“We need you to win back the House of Representatives.

“Above all, we need you to beat Donald Trump and elect Kamala and Tim [Walz].”

Biden’s appearance at the start of the four-day event caps a dramatic handover to his No.2 after he was pressured to quit the race last month by Democrat leaders worried he was too old to win or serve another four years.

Harris appears

Earlier Harris made a surprise appearance, drawing cheers from the crowd as she vowed to defeat Trump on November 5

“Let us fight for the ideals we hold dear and let us always remember, when we fight we win!” she said in brief remarks that drew roars from the crowd.

Harris had been expected to appear later with Biden on the first night of the four-day event in Chicago.

She has ridden a historic whirlwind into the Democrats’ convention: Her campaign has broken records for fundraising, packed arenas with supporters, and turned opinion polls in some battleground states in Democrats’ favour.

While Democrats gathered at United Centre, home to Chicago’s basketball and hockey teams, hundreds of protesters assembled at a nearby park to pressure the party to drop military support for Israel’s offensive in the Gaza Strip.

Harris will formally accept the nomination on Thursday night (US time) with a speech.

-with AAP