US Republican presidential front-runner Donald Trump won a crucial nominating contest in Florida and knocked rival Marco Rubio out of the race on Tuesday, but lost Ohio to John Kasich in a mixed result that set the stage for a long contested race.
Trump, a businessman who had hoped for a five-state sweep that would have put him on the path to the nomination, now faces a tough three-way struggle with Kasich, the Ohio governor, and Ted Cruz, the conservative US senator from Texas.
Kasich won all 66 of Ohio's delegates, giving new hope to establishment Republicans battling to deny the brash New Yorker the nomination and block him from capturing the 1,237 delegates needed to win the nomination at the party's July convention.
On the Democratic side, former Secretary of State Hillary Clinton, 68, won in Florida, Ohio and North Carolina, putting more distance between herself and rival Bernie Sanders, 74, a US senator from Vermont.
The wins for Clinton added to her lead of more than 200 pledged delegates over Sanders and gave her an almost insurmountable edge over him.
"We are moving closer to securing the Democratic Party nomination and winning this election in November," Clinton said at a victory celebration in West Palm Beach, Florida.
Trump's vows to deport 11 million illegal immigrants, impose protectionist trade policies and temporarily ban Muslims from entering the country have rattled the party's establishment and left them scrambling to block him.
Kasich's win will make him the prime hope of the party's mainstream leaders who fear Trump's rowdy campaign will lead the party to defeat in November, replacing Rubio.
"While we are on the right side this year, we will not be on the winning side," Rubio, a first-term senator who is not seeking Senate re-election, told supporters in Miami as he pulled out of the race.
Rubio, 44, said the party's establishment had long looked down on conservatives and taken their vote for granted.
"People are angry, people are frustrated," he said, adding it would have been easy to stir up those frustrations and make people more angry. "I chose a different route and I'm proud of it."
Trump's closest challenger nationally is Cruz of Texas, 45, a favourite of the conservative Tea Party.
Trump, 69, said early on Tuesday that his momentum was already drawing in establishment Republicans who had previously balked at his candidacy but now see him as the likely nominee.
"They're already calling," he told NBC's "Today" show, without naming names. "The biggest people in the party are calling."
By capturing Florida, Trump won all 99 of the state's delegates, giving him a huge lift in his drive to the nomination.