Donald Trump has decisively won Nevada’s Republican caucuses as his main rivals battled for second place in an increasingly urgent effort to slam the brakes on the Trump juggernaut.

Trump now has three straight victories – in the West, the South and Northeast – a testament to his broad appeal among the mad-as-hell voters making their voices heard in the 2016 presidential race.

Six in 10 caucus goers said they were angry with the way the government is working, and Trump got about half of those angry voters, according to preliminary results of an entrance poll on Tuesday night.

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Nevada was a critical test for Marco Rubio and Ted Cruz, the two senators battling to emerge as the clear alternative to the Republican front-runner.

Marco Rubio battling for second place. Photo: Getty

Rubio was out to prove he can build on recent momentum, while Cruz was looking for a spark to recover from a particularly rocky stretch in his campaign.

Rubio, already campaigning in Michigan as caucus results rolled in, was projecting confidence that he can consolidate the non-Trump voters who have been splintering among an assortment of Republican candidates, saying, “we have incredible room to grow”.

Cruz, a fiery conservative popular among voters on the Republicans’ right, finished a disappointing third in South Carolina after spending much of the past two weeks denying charges of dishonest campaign tactics and defending his integrity.

Another disappointing finish in Nevada would raise new questions about his viability heading into a crucial batch of Super Tuesday states on March 1, including his home state of Texas.

Cruz won the Iowa caucuses on February 1 but has fallen behind Trump ever since. Photo: Getty

“There’s something wrong with this guy,” Trump said of Cruz in his typically blunt manner during a massive Las Vegas rally Monday night.

Nevada’s caucusing played out in schools, community centres and places of worship across the state – a process that’s been chaotic in the past.

Nevada marks the first Republican nominating contest in the West and the fourth of the campaign as the candidates try to collect enough delegates to win the party’s nomination at the national convention in July.

Although Nevada has relatively few delegates, it is the first measure of voter sentiment in the vast western region, much as South Carolina was the first glimpse at the South’s preferences last weekend.

Nevada is 28 per cent Latino, nine per cent Asian-American and leads the nation with the highest rate of people living in the country illegally, according to the Pew Hispanic Center.

Its immigrant communities – 19 per cent of its population was born outside the US – have helped turn a once reliably Republican state into one that backed Obama twice.

-AP