US President Joe Biden is set to host a record-breaking fundraiser in New York City, alongside his predecessors Barack Obama and Bill Clinton.

The gathering and concert will raise over $25m (£20m) for the Democrat's re-election campaign - the most ever for a single political event, says his team.

They are looking to extend a growing cash gap between the president and his Republican challenger Donald Trump.

Polls suggest the race for the White House rests on a knife edge.

Thursday's event at New York's Radio City Music Hall comes after a Biden campaign blitz in battleground states that could prove pivotal in November's vote.

The 81-year-old has been seeking to capitalise on momentum following his State of the Union Address earlier this month, which was well-received by Democrats.

However, the president's approval ratings remain persistently low.

Mr Trump is also in the New York area on Thursday, attending the wake of a police officer, Jonathan Diller, who was shot and killed in the line of duty.

The Biden campaign recently declared it had $155m cash to hand, which it said was the biggest war chest any Democratic candidate in history had possessed at this point in an election cycle.

Mr Trump and his political action committees reported having $74m.

Over 5,000 people are expected to attend the star-studded Democratic fundraiser on Thursday night, with many more watching online.

Late-night talk show host Stephen Colbert will moderate a conversation with the three presidents.

The event will be hosted by actress Mindy Kaling and feature musical performances from Lizzo, Queen Latifah and Lea Michele.

First Lady Jill Biden will host an after-party for 500 guests. The president's son, Hunter Biden, and his family are also attending.

The tickets are priced between $225 and half-a-million dollars. For $100,000, guests can get a picture with Mr Biden, Mr Obama and Mr Clinton, with star photographer Annie Leibovitz taking the snaps.

President Biden was joined on the Air Force One flight to New York by Mr Obama, who briefly came back for an off-the-record chat with reporters on the presidential jet.

The two men have remained close since Mr Obama left the White House, and are reported to speak regularly.

New York ground to a halt for their arrival as the two men's huge motorcade cut across Manhattan in the pouring rain as hundreds of onlookers jostled to take pictures.

Mr Biden's previous best single-day fundraising effort was the $10m he raised in 24 hours after his State of the Union address on 7 March.

His fundraising lead over Mr Trump - who is seeking a return to the White House four years after his presidency ended - has been boosted by the advantage of incumbency, experts say.

"Biden raising a lot of money is probably a function of him not having any real primary challengers," Joseph Campbell, a communications professor at American University, told the BBC. "There's no competition for Democratic donor money."

Mr Trump's campaign and his joint fundraising committee brought in $20m in the whole of February, less than what the Biden campaign expects to receive just from Thursday's event.

In addition to Mr Trump's fundraising challenges, his campaign and political action committees have had to spend millions of dollars in legal fees fighting the criminal and civil cases against him.

Mr Trump, 77, blasted the Democratic fundraising event in a fundraising email of his own, sent out by his campaign on Thursday morning.

"Hundreds of deranged Hollywood liberals will be in attendance, and they will open their wallets to fund the destruction of country!" the message said.