Democratic presidential hopeful former vice president Joe Biden (center) arrives on stage with his wife Jill Biden and sister Valerie Biden Owens for a Super Tuesday event in Los Angeles on Tuesday. Photo: AFP

A resurgent Joe Biden seized the momentum in the race to become the Democratic challenger to US President Donald Trump with a string of Super Tuesday victories, including key prize Texas, against rival Bernie Sanders.

Sanders, a 78-year-old leftist who wants to reshape America's economy, had been the clear leader and was looking for a knock-out blow on the most consequential voting day on the primary calendar.

Instead, the results signaled 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.

Just one week ago the 77-year-old senior statesman saw his campaign teeter on the edge of collapse. 

Now he is vying once again for frontrunner status.

"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.

The centrist 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."

A defiant Sanders celebrated his own wins earlier in the night by tearing into Trump, calling him "the most dangerous president in the history of this country." 

But he also attacked Biden for having voted for the invasion of Iraq and painted him as tarnished by billionaire contributors.

"We're taking on the political establishment," he said. "You cannot beat Trump with the same-old, same-old kind of politics."

Biden saw the results as proof that his bid to bring American politics back to the center, after four years of Trump's right-wing populism, is on a roll.

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

AFP