U.S. Republican front-runner Donald Trump warned on Wednesday of riots if he is denied the party's presidential nomination after a string of primary election victories.

The New York billionaire scored big wins in Florida, Illinois and North Carolina on Tuesday which brought him closer to the 1,237 delegates he needs to win the nomination.

But one loss - in the crucial state of Ohio - left the door open for those in the party trying to stop Trump from becoming the Republican nominee for the Nov. 8 election.

Trump might fall short of the majority required, enabling the party establishment to put forward another name at the July convention in Cleveland to formally pick its candidate.

In an interview with CNN on Wednesday, Trump said if he got a large number of delegates yet was denied the nomination: "I don't think you can say that we don't get it automatically. I think you'd have riots. I think you'd have riots. I'm representing many, many millions of people."

Party leaders are appalled at the real estate developer and reality TV personality's incendiary rhetoric and believe his policy positions are out of step with core Republican sentiment, such as his vow to deport 11 million illegal immigrants, temporarily ban Muslims from the United States and build a wall along the border with Mexico.

But the Republican establishment's bid to stop him may have come too late as a field of candidates that once included Trump and 16 high-profile party figures has dwindled to only three with Trump, 69, in command ahead of U.S. Senator Ted Cruz, 45, and Ohio Governor John Kasich, 63, who won the Ohio Republican primary on Tuesday.

While the Republican race remained in turmoil, Hillary Clinton won victories in Florida, Illinois, Ohio and North Carolina on Tuesday that cast doubt on U.S. Senator Bernie Sanders' ability to overtake her for the Democratic Party's nomination.