Bernie Sanders loses lead in Democratic primaries as Joe Biden surges

Despite the surge from his centrist competitor, Sanders celebrated winning California, the biggest win of the primary contest, by a significant margin. 

Tuesday's polls dramatically altered the Democratic Party's presidential field, which featured more than a half dozen candidates a week ago, into a two-horse race.

“People are talking about a revolution. We started a movement," Biden said in Los Angeles, knocking one of Sanders' signature lines.

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Without citing his surging rival by name, Sanders swiped at Biden from Burlington, Vermont.

“You cannot beat Trump with the same-old, same-old kind of politics,” Sanders declared, ticking down a list of past policy differences with Biden on social security, trade and military force. “This will become a contrast in ideas.”

Biden and Sanders, lifelong politicians with starkly different visions for America’s future, were battling for delegates as 14 states and one US territory held a series of high-stakes elections that marked the most significant day of voting in the party’s 2020 presidential nomination fight.

Tuesday’s vote also saw the campaign for media tycoon Mike Bloomberg, who spent $700 million of his personal future on a late-entry bid, sink, as he failed to win a single state. He did achieve a consolation victory in American Samoa, a tiny territory in the Pacific.

Senator Elizabeth Warren also polled poorly, losing her home state of Massachusetts to Biden.

Sanders, a clear favourite among young voters as well as minorities such as Hispanics and Arabs, had been the clear leader so far and was looking for a knock-out blow on the most consequential voting day on the primary calendar.

Instead, the results signalled a remarkable comeback for Biden, a former vice president under Barack Obama who was projected to win at least nine, and possibly 10, of the nomination contests held across 14 states.

Biden also won all of Super Tuesday southern states, indicating his consistent support among black voters, a key constituency for the November election.

Just one week ago, after floundering in the first handful of primary votes, the 77-year-old year old saw his campaign teeter on the edge of collapse.

"It's a good night and it seems to be getting even better! They don't call it Super Tuesday for nothing," Biden told cheering fans in Los Angeles.

Sanders, self-described democratic socialist, was projected to win his home state of Vermont, Colorado, Utah - with exit polls also pointing to a win in the biggest delegate-rich state of all, California.

Biden was projected to win in Virginia, North Carolina, Alabama, Oklahoma, Tennessee, Arkansas, Massachusetts and even Minnesota - a state where Sanders had been expected to win handily.

Well after midnight the projection was made for Biden to win Texas, the second largest US state, and where Sanders had also been polling ahead.

With 94 percent of the southern state's precincts reporting, Biden was ahead of Sanders by nearly four percentage points.

"We expected a surge. We got a tsunami," tweeted analyst David Axelrod, chief strategist for Obama's two presidential campaigns. "New race. Completely."

"We are very much alive," he told a crowd in Los Angeles. "Make no mistake about it, this campaign will send Donald Trump packing."

Agencies contributed to this report.