Donald Trump is already looking ahead to the general election after a new poll showed him narrowly ahead of Hillary Clinton in a hypothetical match-up for the first time in more than six months.

As voters in Indiana go to the polls on Tuesday in a contest that is expected to hand Mr Trump a decisive victory, Mr Trump touted a new poll that for the first time since October put him ahead of the Democratic frontrunner.

Speaking on Monday afternoon to supporters in the city of Carmel, north of Indianapolis, the New York tycoon shared the results of a survey conducted by the Rasmussen Reports which showed him ahead of the former secretary of state 41-39 in a national head-to-head.

(RealClearPolitics (RealClearPolitics)

Mr Trump told his supporters that he had just been handed the news that he was ahead in the national poll, as well as in the polls for the Republican race in Indiana.

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

He added: “It’s a movement. Something is going on. We’re going to straighten it out.”

The poll released on Monday bolstered Mr Trump against claims by his rivals Ted Cruz and John Kasich - both behind him in the polls in Indiana and far behind him in national delegate count - that they would fare better against Ms Clinton in a general election this November.

The poll of 1,000 likely voters was conducted April 27-28, and had a margin of error of 3 percentage points.

Hillary Clinton is also starting to focus on the general election (Reuters)

In Indiana itself, Mr Trump continues to enjoy a roughly nine-point lead over Mr Cruz, according to the RealClearPolitics average.

Speaking to Fox News on Monday night, after his final rally ahead of Tuesday’s vote, Mr Trump repeated what he had said earlier.

“All of the pundits, they’re all saying that ‘it’s over’ if you win Indiana,” he said.

Mr Trump also said that polls ahead of next month’s primary in California had boosted his chances there over Mr Cruz and Mr Kasich. “It looks like I’m going to win California big,” he said.

Mr Cruz, who trails Mr Trump by more than 400 delegates, has said his campaign will continue even if he loses in Indiana, as he hopes to do well in upcoming contests in Nebraska, Oregon and Washington.

At the same time, he has admitted that Indiana’s outcome is vital if he is going to stop Mr Trump securing the 1,237 delegates needed to win the nomination.

Mr Cruz - who was interrupted by noisy Trump supporters at a campaign stop in the city of Marion - insisted on Monday that he still has a path to victory.