Donald Trump easily won Nevada, consolidating his lead in the GOP nomination race.
The Republican hope for president now has three consecutive victories after victories in New Hampshire and South Carolina.
Senators Marco Rubio and Ted Cruz, who attacked each other this week, are vying for second place.
GOP officials said they were considering reports of double voting and a lack of enough ballots in one cabinet.
Some volunteers also wore clothing in support of Donald Trump, but officials said it was not against the rules.
In his victory speech, Donald Trump told a roaring crowd of supporters: “We win, we win, we win the country and soon the country will start winning, winning, winning.”
Nevada, usually a swaying state with a significant Latin population, is crucial to the election process. Hillary Clinton won the state on February 20 in the Democratic race.
About 30 delegates – about 1% of the total – are ready to grab the parliamentary group in Nevada, the first Republican test in the western United States.
Early results show that Donald Trump has a 42% lead over the rest of the Republican group, with his closest rival Marco Rubio receiving 25% of the vote.
In the Democratic group in Nevada last week, Hillary Clinton defeated rival Bernie Sanders by five percentage points.
On February 27, both candidates faced each other in South Carolina, where they focused their campaigns on the black vote.