Donald Trump marched towards a White House rematch with President Joe Biden in November as his final Republican rival Nikki Haley was reportedly set to drop out Wednesday after a heavy defeat in the "Super Tuesday" primaries.

Haley, 52, the former US ambassador to the United Nations under Trump, was about to suspend her campaign, the Wall Street Journal and CNN reported. She was due to speak in Charleston, South Carolina, at 10:00 am (1500 GMT).

Former president Trump swept 14 out of 15 states up for grabs on the biggest day of the 2024 race so far, with Haley denying him only in the northeastern state of Vermont as he covets a second term in the Oval Office.

Incumbent Biden also swept the Democratic "Super Tuesday" primaries, although he was effectively uncontested, and the 81-year-old will now turn his attention to his crucial State of the Union speech on Thursday.

Eyeing a historic comeback to the US presidency, Trump told cheering supporters at his Mar-a-Lago beach club in Florida that they had witnessed "an amazing night and an amazing day."

"They call it 'Super Tuesday' for a reason," said Trump, 77.

"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 South Carolina governor, has failed to throw 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.

Yet his appeal among working-class, rural and white voters, particularly on issues like immigration and the economy, has propelled him toward the nomination in one of the most lopsided primary seasons ever seen.

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.

  Biden v. Trump, again? 

 "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 Monday, clearing the way for Trump's participation in every state.

The states up for grabs Tuesday offered 70 percent 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, had previously argued she is more likely than Trump to beat Biden in November and could forge on.

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

The president raced to clear wins -- minus a loss in tiny Pacific Ocean territory American Samoa -- and warned Trump was "determined to destroy" US democracy.

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

The only real challenge to Biden came from signs of a protest vote over his support for Israel's offensive on Gaza, with some voters filling out ballots saying "uncommitted" in Minnesota and other states.

But Biden faces an uphill battle in November with several recent polls giving Trump a narrow lead, with voters concerned in particular about the president's age, even though Trump is just four years younger.

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.