Joe Biden has won six of the 14 states that voted to pick a Democratic White House candidate on Super Tuesday, in a remarkable rebound for his campaign.
The former US vice-president has swept Oklahoma, Arkansas, Alabama, Tennessee, North Carolina and Virginia.
Left-wing Senator Bernie Sanders is expected to win Colorado and his home state of Vermont.
They lead the race to anoint a Democrat who will face President Donald Trump, a Republican, in November’s election.
Mr Biden, a moderate Democrat, and Mr Sanders, a left-winger, offer starkly different visions for America’s future.
US media are also projecting that Mr Biden has won Minnesota, a day after the Midwestern state’s senator Amy Klobuchar dropped out and endorsed him.
CBS News, the BBC’s US partner, projects Massachusetts is also leaning Mr Biden’s way, a heavy blow to his rival and the liberal state’s own Senator, Elizabeth Warren.
Buoyed by last-minute endorsements from former rivals who dropped out of the race, Mr Biden is hoping to blunt the momentum of Mr Sanders, who was the frontrunner nationally on the eve of the vote.
Mr Biden’s under-staffed and under-funded campaign has been resurgent since his commanding win in South Carolina’s primary at the weekend. It was the first time the 77-year-old had won any contest in three White House runs.
Exit poll data suggests Mr Biden has won large majorities of African-American voters, a crucial bloc for the Democratic party.
Mr Biden also appears to have won convincingly among the type of suburban voters who pollsters say have been turning away from President Donald Trump.
With all precincts reporting, Mr Biden won about 53% of the vote in Virginia, leaving Mr Sanders a distant second on 23%.
Virginia and North Carolina are so important because they are key swing states in the 2020 election.
All eyes now are on the biggest voting state of California and the second-biggest, Texas.
Mr Sanders is hoping to do well in the Golden State, a liberal behemoth, while exit poll data suggests he won 45% of the Hispanic vote in Texas, compared to 24% for Mr Biden.
Also appearing on a presidential ballot for the first time after skipping all four contests last month was Michael Bloomberg.
The former New York mayor, who has spent more than half a billion dollars of his own money, is expected to win the US territory of American Samoa.
Mr Joe Biden aims to consolidate the centrist Democratic vote by barging aside Mr Bloomberg, one of the world’s richest men.
But the billionaire wildcard lowered expectations for his performance ahead of Tuesday, indicating he plans to fight all the way to the party convention in Milwaukee, Wisconsin, in July.
Source: bbc.com