Donald Trump's chances of clinching the US Republican presidential nomination shot to a record high on global betting websites on Wednesday and the billionaire businessman, long viewed as a political outsider, won his first endorsement from a member of Congress.

Trump easily won the Nevada caucuses on Tuesday, giving him his third win in four early nominating contests and pressuring Republican rivals to come up with a way to stop a candidate who only last year was not seen as a serious contender for the Nov. 8 presidential election.

The real estate magnate swept Nevada by a margin of 22 percentage points, winning 45.9 percent of the vote.

It was the high point so far of an unorthodox campaign during which Trump has fought with Pope Francis, called for a temporary ban on Muslims entering the United States and promised to build a wall on the US-Mexican border to prevent illegal immigration.

Trump's Nevada win is likely to further frustrate Republican establishment figures who, less than a month ago, were hoping his campaign as a political outsider was stalled after he lost the opening nominating contest in Iowa to Ted Cruz, a US senator from Texas.

In his victory speech in Nevada, the former reality TV show host courted his base of blue-collar workers.

"I love the poorly educated," he said, mentioning several demographic groups among whom he said he was winning.

By Wednesday, that phrase was being widely discussed online, with some finding it funny and others arguing it was a welcome, non-judgemental embrace of a constituency that other politicians might speak of only as a problem to be fixed.

Trump's nearest rivals, Cruz and Marco Rubio, a US senator from Florida, have frequently attacked each other, clearing a path for Trump to the Republican nomination that includes primary elections in a slew of southern states on March 1, known as Super Tuesday.

"These guys have to figure out how to turn their fire on Trump," said Ford O'Connell, a Republican strategist in Washington. Absent that, he said: "Which one is going to get out of this field?"

Rubio said Trump was only backed by a minority of Republicans.

"The vast and overwhelming majority of Republicans do not want Trump to be the nominee," he told NBC, citing the network's recent opinion poll putting him 15 points ahead of Trump in a one-on-one match-up. "As long as there are four people running dividing up the non-Trump vote sooner, you're going to get results like what you saw last night."

Rubio and Cruz have struggled to match the popularity of Trump, who is more ready than the two senators to deviate from the tenets of the Republican Party's brand of conservatism, including free trade and supply-side economics.

Betting odds

Betting venues in Britain, Ireland and New Zealand show the online wagering community coalescing around Trump, once considered an interloper, attracting long-shot odds of 200/1.

Odds for Trump becoming the Republican candidate for November have tightened all the way to 1/2 in some cases.

"Mr Trump has triumphed yet again, despite political analysts almost unanimously writing him off as a serious presidential contender," said Graham Sharpe from William Hill, adding one customer stood to collect at least $100,000 if Trump was elected to the White House.

On Wednesday, Chris Collins, a Republican congressman from Trump's home state of New York, became the first national lawmaker to endorse Trump, saying in a statement "it's time to say no to professional politicians and yes to someone who has created jobs and grown a business."

While more than 1,200 delegates are needed to secure the Republican presidential nomination, Trump has built a formidable head start over Rubio, who came in second in Nevada with 23.9 percent, and Cruz with 21.4 percent.

Opinion polls show Trump ahead in most Super Tuesday states.

The primary election next Tuesday in Cruz's home state of Texas is looming as a make-or-break moment for him after Trump's growing success among the senator's core base of evangelicals and other conservative supporters.

"Texans have a good ability to see through baloney, to see through a smokescreen, to see through rhetoric and to look to substance," Cruz said at an event in Houston, the state's largest city. "I believe that is exactly what Texans are going to do next Tuesday."