US President Joe Biden and former President Donald Trump appear headed towards a rematch of their 2020 election match up, after millions of Americans on Tuesday voted as part of Super Tuesday, in which 16 states and one US territory held presidential nominating contests in some form.

Over a third of all the available delegates for both the Republican and Democratic nominations were at stake on Super Tuesday.

Biden is the leading contender for the Democratic nomination, and has no substantial primary challenger. Trump entered the day leading former UN Ambassador Nikki Haley in the Republican nomination race, having won all the primaries so far with the exception of Washington, DC.

Haley has vowed to stay in the race through Super Tuesday despite her string of losses in the earlier primaries.

It takes 1,968 delegates to win the Democratic nomination and 1,215 delegates to win the Republican nomination.

So far, Trump has cruised to victory in 11 states, with Haley securing one victory in the state of Vermont.

Live updates:

Tuesday, 11:16 p.m. EST: Trump will win the California Republican presidential primary, where 169 delegates are at stake, CNN projects.

The network also projects that Biden will win the California Democratic primary, with 424 pledged delegates are at stake.

Tuesday, 10:52 p.m. EST: Haley has secured her first Super Tuesday primary victory, having defeated Trump in Vermont, according to multiple projections.

Tuesday, 10:34 p.m. EST: Trump spoke from Palm Beach, Florida, after he was projected to win primary contests in at least 11 Super Tuesday states.

Trump said that "we have a very divided country," and vowed to unify it soon.

He added, "We have a great Republican party with tremendous talent and we want to have unity and we're going to have unity and it's going to happen very quickly."

Tuesday, 10:25 p.m. EST: Fox News projects that Biden will win the Utah Democratic primary.

Tuesday, 9:54 p.m. EST: According to projections, Trump and Biden have won their respective parties’ primaries in Minnesota and Texas.

Tuesday, 9:35 p.m. EST: Biden and Trump have won in both Alabama and Colorado, according to CNN projections.

Tuesday, 8:42 p.m. EST: Biden and Trump have won their respective parties’ primaries in Arkansas.

Tuesday, 8:37 p.m. EST: Biden has won the Democratic primaries in Massachusetts and Maine, NBC News projects.

Trump will win the Tennessee Republican primary, the network said.

Tuesday, 8:13 p.m. EST: Trump has won the Oklahoma Republican primary. Biden has won the Democratic primaries in Oklahoma and Tennessee.

Tuesday, 7:30 p.m. EST: Biden has won the primaries in Vermont and North Carolina, according to NBC News projections.

Trump has won the North Carolina Republican primary, the network projected.

Tuesday, 7:19 p.m. EST: Trump will win the Virginia Republican primary, NBC News projects.

Tuesday, 7:05 p.m. EST: Biden has won the Virginia Democratic primary, NBC News projects.

Tuesday, 6:35 p.m. EST: Biden will win the Iowa Democratic mail-in caucus, multiple US networks projected.

Trump won Iowa in mid-January. Iowa Democrats did not hold their contest at that time after the Democratic National Committee decided to move the vote to later in the primary calendar.