US Republican presidential candidate Donald Trump speaks at a campaign event at The Palladium at the Center for Performing Arts in Carmel, Indiana, US, May 2, 2016. [Photo/Agencies]

INDIANAPOLIS, Ind. - Republican front-runner Donald Trump swept to a commanding victory in Indiana on Tuesday, putting him on a glide path to the party's presidential nomination as Ted Cruz finally ended his campaign.

The New York billionaire won decisively in a state where Cruz, his nearest rival, had hoped to show he was still a factor in the race for the Republican nomination.

Republican National Committee Chairman Reince Priebus called Trump the party's presumptive nominee in a tweet and said, "We all need to unite and focus" on defeating Clinton.

As the vote returns flowed in, Cruz announced that he has ended his campaign at an event in Indianapolis, with his wife, Heidi, at his side. Cruz, 45, sounding beaten but defiant, said he no longer sees a viable path to the nomination.

"Together we left it all on the field in Indiana," said Cruz, a US senator from Texas. "We gave it everything we got. But the voters chose another path, and so with a heavy heart, but with boundless optimism for the long-term future of our nation, we are suspending our campaign."

Trump was on track to take over 50 percent of the vote. Ohio Governor John Kasich was running a distant third.

On the Democratic side, Bernie Sanders was leading Hillary Clinton by a modest margin, but the race was still considered too close to call.