Des Moines, Iowa - Nikki Haley has overtaken Ron DeSantis for coveted second place in the Iowa caucuses, the last poll before voting in the Republican primaries kicks off showed, but former President Donald Trump still leads the field of candidates by nearly 30 percentage points.

The Midwestern state of three million people officially kicks off the 2024 US presidential election on Monday when its residents participate in its unusual "caucus" system to mark their preference for Republican presidential candidates.

Donald Trump received 48% of likely votes in the NBC News/Des Moines Register/Mediacom Iowa poll, which is notable for its historical accuracy and ability to fuel last-minute surges.

Election watchers have been looking for signs of a potential jump by Haley after she steadily gained support throughout the primary election season. She notched 20% of the vote, according to the poll, which is four percentage points up from where she stood in December.

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Florida Governor DeSantis meanwhile fell three percentage points to 16%, it showed.

Iowa is a notoriously poor predictor of the eventual nominee, but it is considered crucial for winnowing the field and as a springboard to the next few battlegrounds.

Those include Haley's home state of South Carolina, as well as her preferred state of New Hampshire, where she trails Trump by only single digits.

Responding to the poll's release, Trump urged his supporters to get out and caucus next week despite frigid blizzard conditions.

"Our grassroots supporters have put us in position to win, and now we have to show up to Caucus for President Trump on Monday and get the job done," he wrote in a statement.

Trump's 28-point lead was down from his 32-point lead over his nearest rival in December.

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Somewhat critically, only 9% of Haley's voters said they were "extremely enthusiastic" for her, while 49% of supporters said that about Trump.

"There is underlying weakness here," J. Ann Selzer, who conducted the poll, said of Haley's standing, according to NBC.

"If turnout is low, it seems to me that a disproportionate share of her supporters might stay at home."