Republican Ted Cruz has won the Wisconsin presidential primary, dealing a blow to frontrunner Donald Trump's hopes of amassing the delegates needed for the party's nomination ahead of the July convention and boosting the chances of a rare contested convention.

Key points: 737 delegates for Trump, 481 for Cruz

737 delegates for Trump, 481 for Cruz Trump 500 short of 1,237 needed to win nomination

Trump 500 short of 1,237 needed to win nomination Democratic contender Sanders wins in Wisconsin, gains momentum against Clinton

Democratic contender Sanders wins in Wisconsin, gains momentum against Clinton New poll shows Cruz about even with Trump nationally

Mr Cruz's win was a breakthrough for Republican Party forces battling to block the controversial New York billionaire, and raised the prospect of a prolonged nominating fight that could last to the July convention.

Democratic presidential contender Bernie Sanders also won in Wisconsin, gaining momentum in his fight against frontrunner Hillary Clinton and trimming her commanding lead in delegates.

Mr Trump had 737 convention delegates to Mr Cruz's 481 heading into the vote, leaving him 500 delegates short of the 1,237 needed to win the nomination.

"The hardworking men and women of Wisconsin stood and campaigned tirelessly to make sure that tonight was a victory for every American," Mr Cruz said after his victory.

"We have a choice. A real choice. The national political terrain began to change two weeks ago.

"In the state of Utah, we won 69 per cent of the vote, a landslide election."

John LeBoutillier, a former New York Republican Congressman, told the ABC that Mr Trump only has himself to blame for his loss in Wisconsin.

"The ethos of Wisconsin politics is they're fairly nice to each other in the Republican Party, and Trump came in there like a bull in a china shop and treated people badly," he said.

"He then goes on radio talk shows which are very popular in Wisconsin and trashed them. This act is not working right.

"Tonight makes it less likely that Trump will be the nominee."

Mr Cruz and Ohio Governor John Kasich, the other remaining Republican contender, hope to stop Mr Trump short of a first-ballot victory and trigger a contested convention.

Mr Cruz, a conservative US Senator from Texas, was aided in Wisconsin by the backing of Republican Governor Scott Walker, who had dropped his own presidential bid in September.

Meanwhile, Mr LeBoutillier described Mr Sander's win as a "huge victory" which will mean trouble for Ms Clinton.

"Hillary lives in New York, yes she was a Senator from New York but she doesn't really fit the democratic primary electorate as well as Sanders does in New York," he said.

"I think this will be a very close race in New York with great peril for Hillary. If she loses her home state I think there's going to be panic in the Democratic Party about her."

Party establishment bands together behind Cruz

Party establishment figures, worried that Mr Trump will lead Republicans to a broad defeat in November, have banded together to try to stop him.

Sorry, this video has expired Ted Cruz celebrates primary win in Wisconsin

The Wisconsin primary followed a difficult week for Trump, who was forced to backtrack after saying women who have abortions should face punishment if the procedure is outlawed, and who voiced support for his campaign manager after he was charged with misdemeanour assault for grabbing a reporter.

A new Reuters/Ipsos poll released on Tuesday showed Mr Cruz about even with Mr Trump nationally, with Mr Cruz's recent gains the first time since November that a Trump rival has threatened his standing at the head of the Republican pack.

In the Democratic race, the win for Mr Sanders, a US Senator from Vermont, is his sixth in the last seven presidential nominating contests, but he still faces a difficult task to overtake Mrs Clinton as the presidential nominating race moves to New York on April 19 and to five other Eastern states on April 26.

Mrs Clinton will head into New York with confidence, currently holding a double digit lead over Mr Sanders.

Reuters/AFP