The former vice-president Joe Biden surged to Super Tuesday victories in nine states, sweeping the south and taking the key state of Texas in a remarkable comeback on the most pivotal night of the Democratic presidential primary race.

His rival, Bernie Sanders, won the crucial state of California, according to the Associated Press, where 415 delegates – more than any other state in the Democratic primary – were up for grabs. Exit polls indicated that the Vermont senator had an approximate 15-point lead, though final results may not be confirmed for days.

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The win gave Sanders a much-needed boost after a rejuvenated Biden swept the southern states of Virginia, North Carolina, Alabama, Arkansas, Tennessee and Oklahoma, propelled by black voters, and scored surprise wins in Massachusetts and Minnesota, before topping the winning streak with the delegate-rich state of Texas.

“It’s a good night and it seems to be getting better,” Biden told supporters in Los Angeles. “They don’t call it Super Tuesday for nothing.”

The two candidates, both in their late seventies, emerged as the frontrunners in the race for the Democratic presidential nomination on Super Tuesday, when 14 states and two US territories had their say. Sanders, a Democratic socialist and the most progressive candidate in the race, represents a starkly different vision for the Democratic party and the country from Biden, a moderate who has run on his record as Barack Obama’s vice-president.

Play Video 1:24 Biden triumphs, Sanders hits back and Warren fights on: how Super Tuesday unfolded – video report

Senator Elizabeth Warren came in a disappointing third place in her home state of Massachusetts and struggled to break through the viability threshold of 15% in other states. Speaking in Detroit, ahead of Michigan’s primary next week, Warren appeared defiant, saying: “You don’t get what you don’t fight for. I am in this fight.”

The California result came in after Sanders took an early home-state win in Vermont as expected, and followed with a win in Colorado and Utah. After the Vermont result, a huge roar went up at Sanders’ Super Tuesday rally in his home town of Burlington, with chants of “Bernie! Bernie! Bernie!”

But Biden’s victories in heavily African American states complemented the former vice-president’s resounding win in Saturday’s South Carolina primary and presented a serious challenge for Sanders, who went into Super Tuesday with a narrow lead.

Facebook Twitter Pinterest Bernie Sanders and his wife, Jane O’Meara Sanders, take the stage during a Super Tuesday rally in Essex Junction, Vermont, on 3 March. Photograph: Chip Somodevilla/Getty Images

The billionaire former New York mayor Mike Bloomberg, who appeared on the ballot for the first time in the Super Tuesday states, did not see his $500m gamble pay dividends.

Bloomberg, who has funneled huge sums of his fortune into his own campaign, won the US territory of American Samoa, which has just six delegates in play, but was poised to receive no delegates in Virginia, where he spent nearly $18m on advertising.

Exit polls also indicated Bloomberg was struggling to clear the 15% threshold required to net delegates in North Carolina, where he spent more than $17m and built a large field operation.

Bloomberg would discuss with his advisers on Wednesday “whether there’s a reason to continue with this”, NBC News reported.

“As the results come in here’s what is clear: no matter how many delegates we win tonight, we’ve done something no one else thought was possible,” Bloomberg said in a 10-minute speech to supporters in West Palm Beach, Florida. “We’ve gone from one per cent in the polls to being a contender for the Democratic presidential nomination.”

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Super Tuesday is the most consequential voting day of the Democratic presidential primary race, with millions of voters across the US casting their ballots for the candidate they want to see take on Donald Trump in the November election.

Sanders headed into this critical day as the frontrunner, well positioned to dominate in California and Texas with the support of energized liberals, young voters and Latinos.

But the race had shifted dramatically in the 72 hours between the South Carolina primary and polls opening on Tuesday, and Sanders was fighting to blunt the sudden rise of Biden, emboldened by a wave of endorsements from the former vice-president’s moderate ex-rivals the Minnesota senator Amy Klobuchar and Pete Buttigieg, the former mayor of South Bend, Indiana, who both dropped out of the race in recent days.

“If we spend the next four months dividing our party and going at each other, we will spend the next four years watching Donald Trump tear apart this country,” Klobuchar said.

Fourteen states, from California to Virginia, and Arkansas to Massachusetts, held primaries on Super Tuesday, as the race moved from a series of intimate, single-day contests to something more akin to a national vote. On Wednesday, nearly 40% of the total delegates to the party’s convention, who eventually nominate the presidential candidate, will have been awarded.

Super Tuesday traditionally has the potential to clarify a dramatically unsettled race. But it was still unclear whether Biden or Sanders would establish a controlling advantage. The uncertainty could pave the way toward a contested convention, the likes of which the party has not seen since 1952.

Sanders, who raised a staggering $46m in February alone, has benefited from a fractured opposition. While Biden, Bloomberg, and, to a lesser degree, Warren, compete for overlapping shares of the Democratic electorate, Sanders has edged past by consolidating support among the party’s left wing.

Facebook Twitter Pinterest Bernie Sanders supporters hold signs during a Super Tuesday rally in Essex Junction, Vermont, on 3 March. Photograph: Charles Krupa/AP

In recent weeks, Democratic leaders and officials have warned that a splintered result on Super Tuesday would put Sanders on a runaway path to the nomination.

But on Tuesday night, Sanders put on the bravest face he could. “I am excited about where we are,” he told supporters. “We have come a long, long way, now let’s go on to the White House.”

Though he didn’t mention the former vice-president by name, he pointedly criticised him over his vote for the war on Iraq and his support for “disastrous trade agreements which cost us millions of good-paying jobs”.

“You cannot beat Trump with the same-old, same-old kind of politics,” Sanders declared.

Democrats award delegates proportionally, dividing the spoils between any candidate who reaches a 15% threshold in a state or its congressional districts. If the result is split, Democrats expect a drawn-out primary race that could last all the way to the party’s convention in Milwaukee in July, where a nominee will be decided.

Perhaps no candidate stood to lose more on Super Tuesday than Bloomberg. His support has more than doubled since his late entry in November, but recent polling suggests he has lost ground after a widely criticized debate performance last month, during which he came under attack for his past comments on women and people of color.

Speaking to reporters from a campaign stop in Miami on Tuesday morning, Bloomberg said his only path to the nomination may be a contested convention.

“I don’t think I can win any other way,” he said, acknowledging that he faced long odds in the 14 states voting on Tuesday. “I don’t know that we’re going to win any.”

American Samoa awarded the long-shot candidate Hawaii congresswoman Tulsi Gabbard one delegate, but that could be enough to secure her place at the next Democratic presidential debate in Arizona, which votes on 17 March with Florida, Ohio and Illinois.

Republican primaries were also taking place on Tuesday, but as Trump does not face any serious competition, the Democratic contest took the spotlight.

Additional reporting by Daniel Strauss in Richmond, Virginia, Richard Luscombe in West Palm Beach, Florida, and Ed Pilkington in Essex Junction, Vermont