US President Joe Biden was joined in New York on Thursday by his predecessors Barack Obama and Bill Clinton at a blockbuster fundraising event where he collected $25 million to go towards his re-election bid.

The Democrat's bumper evening took place at Radio City Music Hall in Manhattan, around an hour's drive from where his Republican rival Donald Trump had earlier attended a wake for a New York police officer killed on duty.

As Biden raked in financial support ahead of November's election, pro-Palestinian demonstrators protested outside the venue -- and several inside the hall whistled and shouted before being ushered away.

Biden's campaign team announced ahead of the event a "record" collection of more than $25 million, noting it was more than Trump had raised for the whole of February.

Thursday's event had a celebrity tinge.

Singers Queen Latifah and Lizzo, among others, warmed up the room before the 42nd, 44th and 46th presidents of the United States sat down for a question-and-answer session moderated by comedian Stephen Colbert. Vogue editor-in-chief Anna Wintour was also in attendance.

The discussion mixed serious topics with jokes, and ended when Obama and Clinton joined Biden in donning aviator sunglasses, Biden's favorite accessory.

Trump's campaign spokesperson, Steven Cheung, had blasted on social network X the "glitzy fundraiser... with their elitist, out-of-touch celebrity benefactors."

- 'Numbers don't lie' -

Earlier in the day, Trump made a short statement after attending the wake of police officer Jonathan Diller, who was shot and killed on Monday during a traffic stop.

"We have to stop it. We have to get back to law and order," said the 77-year-old billionaire, who refrained from criticizing his 81-year-old rival directly.

Trump devotes much of his campaigning to attacks on illegal immigration and criticizing Biden for being lax on policing.

The White House said Biden had called New York Mayor Eric Adams on Thursday to offer his condolences over Diller's killing.

The Democrat has not been in contact with the officer's family but "grieves" with them, his spokeswoman Karine Jean-Pierre said, adding that the president "has stood with law enforcement his entire career and continues to stand with them."

Jean-Pierre said on Wednesday that Biden was "deeply grateful for the sacrifices police officers make to keep our communities safe."

Biden and Trump, who faced off at the ballot box in 2020, are guaranteed to win their respective parties' nominations for the November presidential election this summer.

The star-studded fundraiser for Biden, however, underscored his party's ability to drum up cash.

According to NBC News, guests at the event could pay $100,000 for a photo with the trio.

"The numbers don't lie: today's event is a massive show of force and a true reflection of the momentum to reelect the Biden-Harris ticket," Jeffrey Katzenberg, the campaign's chief fundraiser, said in a statement, referring to Vice President Kamala Harris.

Biden has better-stocked campaign coffers than his Republican opponent, who is using some of the funds raised from his supporters for legal expenses in the multiple court cases he is facing.

Trump's trial for allegedly covering up 2016 hush money payments to a porn star when he was running for his first term in office begins in New York on April 15.