The prospect of a President Trump has come one step closer after the billionaire celebrated a huge victory in the lastst US primary.

His victory in the Indiana Primary was so decisive that his Republican rival Ted Cruz announced he was dropping out of the race.

That means it is all but certain Mr Trump will face off against Hillary Clinton in the general election.

In his victory speech, Mr Trump declared: "We’ve been losing all the time, we lose with our military, we can’t beat Isis, we lose with trade, we lose with borders, we lose with everything.

“We’re not going to lose, we are going to start winning again – and we’re going to win bigly.”

Mr Trump then added a muted compliment to Mr Cruz. “I don’t know if he likes me or doesn’t like me, but he is one hell of a competitor. He has an amazing future and I want to congratulate him,” he said.

Mr Trump had gone into Tuesday’s race with a lead of perhaps six or seven points according to the polls. Yet, within minutes of the polls closing at 7pm, a flurry of US broadcasters called the race for the New York tycoon.

With more than 60 per cent of the polls having been counted, Mr Trump 53 points, with Mr Cruz on 37 and John Kasich trailing in third place on eight points.

In the Democratic race, Hillary Clinton lost to Bernie Sanders by 51-49. While Ms Clinton had gone into the day with polls suggesting she had a lead of six or seven points, on Tuesday morning her campaign had repeatedly said it was bracing for a loss.

Yet, the former secretary of state has a huge advantage over the Vermont senator and most observers believe it is only a matter of time before she gathers sufficient delegates to call the nomination hers.

Donald Trump had said 'the race was over' if he won in Indiana (AP)

Mr Trump was quick to turn to Twitter to celebrate his win. “Thank you Indiana,” he said, before he preparing for a victory rally at Trump Tower in New York.

At Crowne Plaza hotel in Indianapolis, supporters of Mr Cruz had gathered hoping they would have something to cheer. Yet very quickly the mood turned to one of sadness and despair.

At around 8.30pm Mr Crump and his running mate, Carly Fiorina, took to the stage. At first it appeared Mr Cruz was preparing to announce he was fighting on, but social media was already reporting - based on information from his campaign manager - that he was about to terminate his campaign.

When the end came, many of his supporters appeared in disbelief.

“Americans are desperate for change,” he said, to cheers and applause.

“I said I’d stay in as long as there was a viable chance to victory.

"Tonight I’m sorry to say, there is not. We gave it everything we got. But voters decided differently.”

He added: “It is with a heavy heart, but with boundless optimism for the future of out nation, that we are suspending our campaign.”

The results arrived after a campaign in Indiana that was never less than strange and a which ended in a utterly bizarre day that saw Mr Trump and Mr Cruz hurt insults and jibes at each other.

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Mr Trump had fired things up by repeating to Fox News, a claim made in the supermarket tabloid, the National Enquirer, that Mr Cruz’s father was somehow somehow involved in the assassination of President John F Kennedy.

“His father was with Lee Harvey Oswald prior to Oswald’s being - you know, shot. I mean, the whole thing is ridiculous,” Mr Trump said.

“What is this, right prior to his being shot, and nobody even brings it up. They don't even talk about that. That was reported, and nobody talks about it.”

Mr Cruz was unable to contain his rage when he was informed of the tycoon’s comments. “While I'm at it, I guess I should go ahead and admit, yes, my dad killed JFK, he is secretly Elvis and Jimmy Hoffa is buried in his backyard.”

He said that Mr Trump was an “utterly amoral... narcissist”, “a pathological liar” and a “serial philanderer”.

Mr Trump had said over the weekend that he considered the race would be decided if won in Indiana, with its haul of 57 delegates, 30 of them on a winner takes all basis and the remainder by Congressional district.

Speaking in the city of Carmel on Monday, he continued with this theme.

“We’re doing great,” he said of his campaign. “If we win in Indiana, it’s all over. We have a very easy path.”