George Clooney has issued a damning call for Joe Biden to quit the US presidential race, hours after senior Democrat Nancy Pelosi swerved questions about whether he should continue.

The Hollywood actor and prominent Democratic fundraiser said that the president had won many battles in his career, "but the one battle he cannot win is the fight against time".

His comments came after Mrs Pelosi, the former House Speaker, joined growing disquiet in the party, saying that time was "running short" for Mr Biden, 81, to decide whether to stay in the race after his stumbling debate against Donald Trump.

The president has stated, repeatedly, that he is determined to remain as the Democratic party's candidate and beat Trump, 78, in November.

Clooney wrote in the New York Times that it was "devastating to say it", but the Joe Biden he met at a fundraising event three weeks ago was not the Biden of 2010. "He wasn’t even the Joe Biden of 2020," added the actor.

"He was the same man we all witnessed at the debate," Clooney said.

The fundraising event, co-hosted by Clooney in Los Angeles and also featuring Julia Roberts and Barbra Streisand, brought in a single-night record of roughly $30m (£23m) for the Biden campaign.

The Biden camp has hit back at the Hollywood star, with an unnamed source telling US media: “The President stayed for over 3 hours [at the fundraiser], while Clooney took a photo quickly and left.”

The president's campaign also pointed out that when he attended the fundraiser he had just arrived in Los Angeles from Italy, where he had been at the G7 summit.

In his op-ed, Clooney said: "Our party leaders need to stop telling us that 51 million people didn’t see what we just saw."

"This is about age. Nothing more," he continued. "We are not going to win in November with this president."

Clooney added that his concerns matched those of "every" member of Congress with whom he had spoken.

Asked to respond, Mr Biden's campaign referred to a letter the president sent Democrats in Congress that said he was "firmly committed" to his candidacy and beating Trump.

Yet public dissent continues to grow within Mr Biden's party as he faces scrutiny while hosting the Nato summit in Washington.

Mrs Pelosi, a highly influential voice among Capitol Hill Democrats, on Wednesday appeared to disregard Mr Biden's insistence that he was determined to forge on.

When asked if he should stay in the election race, she told MSNBC's Morning Joe: "I want him to do whatever he decides to do.

"It's up to the president to decide if he's going to run. We are all encouraging him to make that decision, because time is running short."

Acknowledging the demands on the president during the Nato summit, Mrs Pelosi told MSNBC: "I said to everyone - let's just hold off.

"Whatever you're thinking, either tell somebody privately, but you don't have to put that out on the table until we see how we go this week. But I am very proud of the president."

Around a dozen elected Democrats have suggested he abandon his campaign since his 27 June debate with Trump.

On Tuesday night, Michael Bennet of Colorado became the first Democratic senator to publicly dissent.

Although he did not call for Mr Biden to quit outright, he said Trump would win the election, possibly by a "landslide".

On Wednesday afternoon, Peter Welch of Vermont became the first Senate Democrat to openly call on Mr Biden to withdraw, "for the good of the country", as he wrote in a Washington Post op-ed.

Democratic Senator Richard Blumenthal of Connecticut told reporters he was "deeply concerned" about Mr Biden's ability to win the election.

Pat Ryan, a congressman from New York, earlier in the day told the New York Times: “For the good of our country, for my two young kids, I’m asking Joe Biden to step aside."

The Biden campaign repeated the president's statement that he was "running this race to the end".

Democratic House Minority Leader Hakeem Jeffries plans to speak to Mr Biden by Friday to discuss the concerns brought by several congressional party members.

Overall support from elected Democrats remains robust, however.

Gavin Newsom, the California governor who was named by Clooney as a potential replacement, said he was still “all in” with Mr Biden.

The Congressional Black Caucus, a group of roughly 60 politicians, and progressive House members like Alexandria Ocasio Cortez, have publicly backed Mr Biden.

On Tuesday, Chuck Schumer, the leading Democrat in the Senate, said: "I'm with Joe." Axios, however, reports that Mr Schumer has been privately telling donors he is open to dumping Mr Biden.

Two unnamed senior Democrats, speaking to CBS News, the BBC's US partner, said there had been a "convergence" of opinion over the last 24 hours between elected Democrats, donors and groups that support the president's party.

One of the sources said all of the interests have reached “a near consensus” about what Mr Biden should do.

Questions about the Democrat's campaign were also swirling at the Nato summit in Washington DC.