Joe Biden has won eight of the 14 states that voted to pick a Democratic White House candidate on Super Tuesday, a remarkable rebound for his campaign.
The ex-US vice-president has swept Massachusetts, Minnesota, Oklahoma, Arkansas, Alabama, Tennessee, North Carolina and Virginia.
But Bernie Sanders is being projected to win the biggest prize of the night, California, and three other states.
They lead the race to face Republican President Donald Trump in November.
Virginia and North Carolina are crucial because they are key swing states in the 2020 election.
With all precincts reporting, Mr Biden won about 53% of the vote in Virginia, leaving Mr Sanders a distant second on 23%.
Exit poll data across the board 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 the current US president.
“We are very much alive,” Mr Biden told a crowd in Los Angeles. “Make no mistake about it, this campaign will send Donald Trump packing.”
