Las Vegas, Nevada - Donald Trump strolled to victory in the Nevada caucus on Thursday, adding more delegates in his seemingly unstoppable march to the Republican Party's presidential nomination.

Trump was the only major candidate on the ballot when party members gathered in public buildings across the southwestern state to cast their in-person votes.

Early results showed the former president had massively out-polled his long-shot challenger, a businessman from Texas, and major US networks said Trump would scoop the state's available delegates.

It was the second go around in presidential preference voting for Nevada this week.

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State-organized primary polls were held on Tuesday in which Nikki Haley was beaten into second place on the Republican ballot by "None of these candidates" – widely seen as a proxy vote for Trump.

That result, however, was meaningless, with Nevada's GOP declaring months ago it would award its delegates from Thursday's rival caucus, a format that strongly favors Trump.

Haley badly trails Trump in the overall race for the nomination, and is on course for another drubbing in her home state of South Carolina later this month.

The former UN ambassador insisted Wednesday that she was not dropping out.

"I'm in this for the long haul," she told supporters at a campaign event in California on Wednesday night, according to The New York Times.

"This is going to be messy, and this going to hurt, and it's going to leave some bruises, but at the end of the day, I don't mind taking them, if you will go right along with me."

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Trump on Thursday said he thought her continued candidacy was not a good idea, but it didn't bother him.

"I don't know why she continues, but let her continue," he said. "I don't really care."

"I think it's bad for the party. I think it's actually bad for her."

Republicans in the US Virgin Islands were also caucusing on Thursday.

Although it is not a state and will not get a say in November's presidential election, the territory does play a part in deciding presidential nominees.

Trump won the party vote by a margin of three-to-one over Haley, giving him all available delegates for the July 15-18 Republican National Convention in Wisconsin, which will decide the nominee.