Palm Beach, Florida - Donald Trump celebrated an "amazing night" as he closed in on the Republican presidential nomination with easy wins in the Super Tuesday primaries, setting up an all-but-certain rematch with President Joe Biden in November.

Fifteen states and a US territory staged nominating contests on the biggest day of the 2024 race so far, with both candidates coveting a second term in the White House.

Texas and California were among the major victories for Trump over Nikki Haley as he picked up support in every demographic, taking conservative southern states and more liberal battlegrounds such as Virginia, one of his longshot challenger's best chances.

He was denied a clean sweep, with Haley edging a tight contest in the northeastern state of Vermont, but the former president told supporters they had witnessed "an amazing night and an amazing day."

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"They call it 'Super Tuesday' for a reason," Trump told a cheering crowd at his Mar-a-Lago beach club in Florida.

"This is a big one. They tell me, the pundits and otherwise, that there has never been one like this, never been anything so conclusive."

This year's Super Tuesday was sapped of much of its suspense as Biden and Trump had effectively secured their parties' nominations before a ballot was cast Tuesday.

Haley, a former UN ambassador, has failed to throw any significant obstacles in Trump's path to the nomination since finishing a distant third in the opening contest in Iowa in January.

Impeached twice, beaten by seven million votes in 2020 and facing 91 felony charges in four trials, Trump has a profile unlike any US presidential election candidate in history.

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Yet his appeal among working-class, rural, and white voters has propelled him toward the nomination in one of the most lopsided primary seasons in modern history.

Haley – a favorite of affluent, suburban voters and university graduates – was set to collect only a handful of the delegates needed to secure the nomination.

"I expect Nikki Haley to finish and drop out. There is no pathway after tonight for her to get the nomination," Kenny Nail, a grassroots Republican activist, told AFP at Trump's Florida watch party.

Trump's victories included Maine, one of three states that had sought to keep him off the ballot over his push to overturn the 2020 election and the assault on the US Capitol.

The Supreme Court rejected the expulsion effort on Monday, clearing the path for Trump's participation in every state.

The states up for grabs Tuesday offered 70% of the delegates Republicans need to be named the party's candidate at the summer convention.

Trump was not able mathematically to close out the contest but he expects to be anointed by March 19 at the latest, according to his campaign.

Haley, who set low expectations ahead of Super Tuesday, traveled to Charleston, South Carolina, to watch the results but wasn't expected to speak and scheduled no events for Wednesday.

Some primary-watchers expect the 52-year-old to end her campaign shortly, though she argues that she is more likely than Trump to beat Biden in November and could forge on.

"There remains a large block of Republican primary voters who are expressing deep concerns about Donald Trump," her spokesperson said late Tuesday.

Biden was on the ballot in the Democratic primaries, but he faced little threat from two outsider challengers, Congressman Dean Phillips and Marianne Williamson, making his re-nomination a formality.

He is due to deliver the annual State of the Union address to Congress on Thursday, a chance to lay out his campaign platform.

The 81-year-old raced to clear wins – minus a loss in the tiny Pacific Ocean territory of American Samoa – and warned that Trump was "determined to destroy" US democracy.

Trump will "do or say anything to put himself in power," Biden said in a statement released by his campaign.

Stephanie Perini-Hegarty voted for Biden in Quincy, Massachusetts.

"I think we need a leader who is not involved in any corruption, and who is going to look out for the best interests of the people," the 55-year-old told AFP.

As he seeks to sew up the nomination, Biden is facing growing frustration from his own base over his continued support for Israel's war on Gaza.