Celebrities praise Joe Biden and rally round Kamala Harris

"There is nothing more important for our country than defeating Donald Trump at the ballot box," said De Niro, a fervent Trump critic.

Oscar-winning actress and singer Barbara Streisand praised Mr Biden, saying he would "go down in history as a man who accomplished significant achievements in his four-year term", in a post on X.

He helped restore "honesty, dignity & integrity to the office after four years of lies, crime, scandal & chaos", according to Star Wars actor Mark Hamill, referring to his predecessor Mr Trump's time in the White House.

This was reiterated by director Ken Burns, who said Mr Biden had "led the country out of the disastrous term of his predecessor [while] quietly doing good things for all Americans".

Singer John Legend said he was "grateful for the grace and patriotism" Mr Biden had shown in stepping aside, and threw his support behind Ms Harris: "She's ready for this fight and I'm excited to help her in any way I can."

Ms Harris has a "trusted and tested" record, according to actress Jamie Lee Curtis, adding that she has been a "fierce advocate for women's rights and people of colour and her message is one of hope and unity for America at her time of great national divide".

If she goes on to win in November's election, Ms Harris would become the first woman, and woman of colour, to win the presidency of the United States.

"Let's make history!!!", comedian Kathy Griffin posted on X, while singer Katy Perry shared a video on Instagram where she sings "It's a woman's world, and you're lucky to be living in it" - a reference to her latest single.

Star Trek actor George Takei said the potential election match-up was now "prosecutor vs felon" - referencing Ms Harris' previous career as a prosecutor, and Donald Trump's conviction on 34 charges for falsifying business records.

Also appearing to back the vice president is singer Charli XCX, who posted on X: "kamala IS brat".

That's a reference to the singer's latest album 'Brat', which has become a social media trend, with supporters tweeting videos of Ms Harris remixed with Charli XCX's music.

Kamala HQ - the official X page of Ms Harris' campaign - has jumped on to the trend too, changing its cover photo to match the colour and style of the Brat album cover.

Hollywood has long been a cash cow for the Democrats, but has turned away from President Biden in recent weeks.

Several big names publicly withdrew their support from his campaign and called for him to be replaced.

One of those is Aaron Sorkin - the creator of US political drama The West Wing - who in a New York Times opinion piece, external published hours before Mr Biden's announcement, called on Democrats to nominate Mitt Romney - a well-known Republican senator and previous Republican presidential candidate.

He has since rowed back, saying: "I take it all back. Harris for America!" in a post published on his behalf on West Wing actor Joshua Malina's X account.

Another is actor George Clooney, who earlier this month reiterated his "love" for Joe Biden in a New York Times opinion piece, external, but said his age and public gaffes on the campaign trail meant "we are not going to win in November with this president".

Mr Clooney has yet to comment since Mr Biden stepped aside.