Republicans in Wild West White House showdown in Nevada

Republican presidential candidate Donald Trump speaks at a rally at the Nugget in Nevada.
Republican presidential candidate Donald Trump speaks at a rally at the Nugget in Nevada.PHOTO: AFP

LAS VEGAS (AFP) - US Republican presidential candidates face off in Nevada with front runner Donald Trump's rivals seeking to break his momentum before next week's all-important "Super Tuesday" votes.

Mr Trump, the billionaire real estate mogul whose name is lit up on a glitzy hotel on the Las Vegas Strip, is the man to beat as he seeks a third straight win after New Hampshire and South Carolina, victories that cemented his status as the party frontrunner.

The contest which gets underway on Tuesday evening (Wednesday morning Singapore time) will be the fourth for the Republican presidential candidates, with Mr Trump so far triumphing in all states but Iowa where he came second.

Although the caucus in Nevada is not expected to have a significant impact on the race - only 30 delegates or slightly more than one per cent of the total are up for grabs - it is the first contest for the Republicans in the US West.

In addition, Nevada has a significant Hispanic population of 27.8 percent. And while they may not be the determining factor - most Hispanics in the state are believed to lean Democrat - they account for the largest bloc of Latino voters to date in the nominations race.

Tuesday's caucus vote is taking place amid increasing recognition that Mr Trump, the political outsider who blasts the Washington establishment as incompetent, may well end up the party's nominee.

He has consistently held a double-digit lead here. The latest CNN/ORC poll, released last week, shows him with 45 per cent support, followed by Senator Marco Rubio a distant second at 19 per cent, and Senator Ted Cruz with 17 per cent.

The race's remaining two Republicans, retired neurosurgeon Ben Carson and Ohio Governor John Kasich, earned seven per cent and five percent respectively.

But Mr Trump has alienated Hispanic voters with his anti-immigrant rhetoric, and it remained unclear whether he will reach such heights in Tuesday's caucus in the Silver State.

He continued to clash with his Republican rivals in the run-up to the Nevada vote, hitting out at Mr Cruz's campaign tactics on Monday, describing his opponent as "sick" and slamming a heckler who disrupted his Las Vegas rally.

"I'd like to punch him in the face," Mr Trump said of the protester.

Mr Cruz fired back on Tuesday accusing Mr Trump of consistently vacillating on issues.

Mr Rubio, who has received a flood of endorsements from fellow lawmakers who see him as the mainstream candidate who can topple Mr Trump, for his part urged registered Republicans in Nevada to turn out in force for the caucus.

"I need your vote tonight!" he said.

The Republican field, which once stood at 17, has shrunk to five. Mr Jeb Bush was the latest to pull out on Saturday following his poor showing in South Carolina.

As the field of candidates narrows, Mr Trump's seemingly unstoppable momentum has mainstream Republicans increasingly on edge about him winning the nomination.

Ms Katie Packer Gage, who heads Our Principles, a political action committee aimed at derailing Trump, said in a memo that "it's critical we come together to prevent Donald Trump from becoming the GOP nominee."

"He is, to put it simply, a conservative of convenience - as his own words and actions over the past 30 years have made abundantly clear," she wrote.

Mr Cruz said there were only three viable Republican candidates left, and "at this point here in Nevada, it's all about turnout."

The real test on where the presidential candidates stand will come on March 1, when 12 states go to the polls.

The Nevada vote takes place between 5.00 pm (9.00 am Wednesday, Singapore time) and 9.00 pm, with results expected after caucuses close.

Unlike primaries, caucuses allow participants to openly engage with one another and hear arguments from candidates' supporters or surrogates, in meetings at schools, community centers and churches.

Republicans then vote by secret ballot, in 130 caucus sites across Nevada.

The results will be used to determine the number of Republican delegates who represent the state at the party's nominating convention in July.