Despite voters in some precincts waiting hours to cast their ballots after polls were set to close, Joe Biden is expected to win the Democratic primary in Texas, securing his share of the second-largest trove of delegates on Super Tuesday.

The former vice president's win in the state was supported by undecided late voters who ultimately backed Mr Biden.

According to exit polls, nearly half of voters who picked their candidate in the last few days supported Mr Biden, while one in five of those voters - representing roughly a quarter of the Democratic electorate - backed Bernie Sanders, who was narrowly defeated in the state after securing California, home to the largest share of delegates.

Former Texas congressman Beto O'Rourke, who dropped out of the presidential race late last year, gave Mr Biden a last-minute endorsement on Monday, potentially giving him a boost as he collected endorsements from other former opponents Pete Buttigieg and Amy Klobuchar.

Voters queued for hours, some as long as five hours after polls had already been scheduled to close, though people in line were able to cast their ballots once they made it in line before the deadline.

The state holds 228 delegates, the second-most after California. Voting officials will take some considerable time to divvy up delegates as they parse through votes.

Though he effectively "won" the state, his share of delegates in the delegate-rich state will likely be smaller than in states where he over-performed.

NBC News estimates Mr Biden will pick up 30 delegates, while Mr Sanders will net 23.

More than 1,300 delegates are up for grabs on Super Tuesday, representing a third of delegates through the primary season ahead of the Democratic National Convention to select the nominee to face Donald Trump in November.