Detroit, Mar 10 (AFP) Surging US presidential candidate Joe Biden has urged Michigan voters to help him bolster his lead over Bernie Sanders as the rivals made their final pitches hours before the battleground state holds its Democratic primary.

The veteran politicians -- Biden a moderate former vice president and Sanders a leftist senator calling for nothing less than a political revolution -- are locked in a political duel to decide who faces President Donald Trump in the November election.

Michigan is the top prize with the largest number of delegates at stake among six states, and the candidates campaigned heavily here.

While Sanders is desperate to right his listing ship with a strong showing, Biden is riding high, having won 10 of 14 states that voted last Tuesday, and was hoping to continue the momentum.

"Michigan, I'm counting on you in a big way!" Biden told a cheering crowd at a majority black high school in Detroit.

Biden, 77, is flush with the endorsements of several high-profile former rivals in the Democratic race, including two prominent African-American senators: New Jersey's Cory Booker, who threw his support behind Biden early Monday, and Kamala Harris of California.

Both lawmakers are touted as possible vice presidential picks for Biden.

Michigan "could be the turning point" of the campaign, Booker said at a Biden rally in Flint.

Later in Detroit, he implored Michiganders to get out the vote on Tuesday to help secure a Biden victory.

"We can't pray he wins, we can't hope he wins, we can't wish that he wins," Booker said. "We've got to vote him in."

Biden took the stage with Booker, Harris and Michigan Governor Gretchen Whitmer, hugging each of them before the quartet held hands and raised them triumphantly aloft.

Biden, who served eight years as deputy to Barack Obama, America's first black president, has repeatedly warned that Americans were not looking for a revolution -- a jab at Sanders, the 78-year-old self-described democratic socialist.

In Detroit, he pushed his Rust Belt roots, highlighted his extensive work in Michigan and reprised his blue-collar message that he honed earlier in the race.

"Wall Street didn't build America, you built America," Biden said. "Unions built the middle class."

Sanders also campaigned in Detroit on Monday and held a roundtable with experts on the coronavirus, which has left at least 26 people dead in the United States and sent stock markets plunging.

Sanders criticized Trump's handling of the crisis, saying the president's "reckless statements are confusing people in this country and all over the world."

Biden made no mention of coronavirus at the Detroit rally, but his campaign made several bottles of hand sanitizer available to attendees.

Biden has surged since scoring a decisive victory in the South Carolina primary on February 29, with endorsements from key African-American leaders helping him claim the frontrunner mantle in the race.

Former Democratic candidates Pete Buttigieg, Amy Klobuchar, Michael Bloomberg and Beto O'Rourke have also swung behind Biden, seeing a moderate as having the best chance of defeating Trump.

Tuesday's primaries will be the first one-on-one duel between Biden and Sanders since all the other major candidates, including Senator Elizabeth Warren, dropped out of the grueling nomination battle that began more than a year ago.

Besides Michigan, Democrats will also be voting in Idaho, Mississippi, Missouri, North Dakota and Washington state.

Michigan is shaping up as a must-win for Sanders, who narrowly won the state over Hillary Clinton during his failed 2016 bid for the Democratic nomination.

The latest polls for Michigan, however, have Biden with a lead of between 15 and 20 points.

The latest Missouri poll has Biden up by nearly 19 points, while he leads Sanders by a narrow two-point margin in Washington. (AFP)

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