Bernie Sanders has surged to the top of a new national poll of Democratic candidates, as support for Joe Biden has tumbled.

On the eve of the New Hampshire primary, the second opportunity for people to actually cast a vote rather simply be questioned by pollsters, the ​Quinnipiac University poll put the veteran Vermont senator on 25 points.

At the same time, the poll, conducted after Mr Biden’s poor fourth place showing in Iowa, had the former vice president down 9 points to 17.

Michael Bloomberg, the former New York mayor who has spent millions of dollars of his own money, stormed to third place, ahead of Elizabeth Warren and Pete Buttigieg.

“Biden scrambles to bounce back in frigid New Hampshire after an icy slide to 17 percent, his lowest national number,” said Quinnipiac University poll analyst, Tim Malloy.

Democratic candidates compete on the campaign trail: In pictures Show all 18 1 /18 Democratic candidates compete on the campaign trail: In pictures Democratic candidates compete on the campaign trail: In pictures Jessica Canicosa, a precinct captain for Bernie Sanders, waits to greet caucus voters at Liberty High School in Henderson, Nevada REUTERS Democratic candidates compete on the campaign trail: In pictures Hotel workers at the Bellagio in Las Vegas get to grips with voting papers during the Nevada caucuses AFP via Getty Images Democratic candidates compete on the campaign trail: In pictures A caricature of Bernie Sanders is projected on to a tree during a rally in Las Vegas EPA Democratic candidates compete on the campaign trail: In pictures A woman waits to have a photo taken with Elizabeth Warren during a town hall meeting in Las Vegas REUTERS Democratic candidates compete on the campaign trail: In pictures The threat of coronavirus and other germ-borne illnesses was on some voters' minds at the Democratic caucuses in Henderson, Nevada Getty Images Democratic candidates compete on the campaign trail: In pictures Former vice-president Joe Biden takes a selfie with a voter in Las Vegas ahead of the Nevada caucuses REUTERS Democratic candidates compete on the campaign trail: In pictures Amy Klobuchar changes her shoes backstage after giving a speech in Exeter, New Hampshire AFP/Getty Democratic candidates compete on the campaign trail: In pictures A warmly-wrapped-up dog attends an Elizabeth Warren event at Amherst Elementary School in Nashua, New Hampshire AFP/Getty Democratic candidates compete on the campaign trail: In pictures Bernie Sanders, who romped to victory in New Hampshire against Hillary Clinton in 2016, talks to the media in Manchester Getty Democratic candidates compete on the campaign trail: In pictures Joe Biden was hoping to improve on his poor showing in Iowa in the New Hampshire primary Reuters Democratic candidates compete on the campaign trail: In pictures Elizabeth Warren, renowned for giving time to supporters for selfies, works the crowd at the University of New Hampshire in Durham Getty Democratic candidates compete on the campaign trail: In pictures Joe Biden takes a selfie with a supporter and his child outside a campaign event in Somersworth, New Hampshire on 5 February Reuters Democratic candidates compete on the campaign trail: In pictures Elizabeth Warren and Bernie Sanders quarrel after a confrontation in a TV debate in which Sanders claimed that Warren was not telling the truth about a conversation in which she claimed he had said a woman could not win the presidency on 14 January AP Democratic candidates compete on the campaign trail: In pictures Supporter Pat Provencher listens to Pete Buttigieg in Laconia, New Hampshire on 4 February Getty Democratic candidates compete on the campaign trail: In pictures Pete Buttigieg speaks at a campaign event in Concord, New Hampshire while awaiting the results of the Iowa caucus Reuters Democratic candidates compete on the campaign trail: In pictures Elizabeth Warren is presented with a balloon effigy of herself at a campaign event in Nashua, New Hampshire on 5 February Reuters Democratic candidates compete on the campaign trail: In pictures A Trump supporter rides past a rally for Amy Klobuchar in Des Moines, Iowa on 14 January AP Democratic candidates compete on the campaign trail: In pictures A man holds up a sign criticising billionaires in the presidential race in front of Michael Bloomberg in Compton, Califronia. The former New York mayor skipped the first caucus in Iowa and instead campaigned in California on 3 February Reuters

“Is the Bloomberg camp prepping the white horse for him to ride to the rescue? Maybe not yet, but without setting foot in Iowa or New Hampshire, he is suddenly a looming shadow over the primary field.”

Meanwhile, another poll, appeared to underscore the challenges facing Mr Biden.

The Reuters/Ipsos poll released on Monday, suggested 17 per cent of registered Democrats and independents would vote for Mr Biden, down five percentage points from a similar poll that ran last week before Iowa held its first-in-the-nation nominating contest.

Pete Buttigieg and Bernie Sanders claim Iowa wins despite results delay

Mr Sanders led other candidates in the poll with 20 per cent of support, up one point from last week, while 15 per cent supported Mr Bloomberg, an increase of six points.

The poll put Ms Warren on 11 points with Mr Buttigieg on 5. The poll had Andrew Yang on 5 points and Amy Klobuchar on 3.

The poll underscored what has been a steady decline in support for Mr Biden, who until recently was considered the favourite to win the highly contested race for the party’s nomination.

Mr Biden’s primary appeal to voters has been his claim to be the most electable of all of the candidates. Yet he finished in fourth place in Iowa, behind Mr Sanders, Mr Buttigieg and Ms Warren.