Republican front-runner Donald Trump rolled to victory Tuesday in the presidential primary in his home state of New York, while Democratic front-runner Hillary Clinton was projected to win her party's contest in the state she also calls home.

The results were based on partial returns and projections by US cable television networks, citing exit polls. Final results were expected late Tuesday.

Trump had confidently predicted victory in the third-largest prize in the state-by-state nominating process, and the win puts him closer to the outright majority of delegates needed to secure the conservative party's nod at its convention later this year.

Trump won in the state where he was born and where the billionaire built much of his real estate and entertainment empire. With 90 per cent of the votes counted, he had 60 per cent.

"We are really, really rocking, and we expect we are going to have an amazing number of weeks," the candidate, flanked by his family, told supporters at his opulent Trump Tower.

He announced imminent travel to some of the five states holding primaries on April 26.

Ohio Governor John Kasich was a distant second at 25 per cent, with US Senator Ted Cruz of Texas at 15 per cent.

Trump's final margin of victory will be decisive in the number of delegates he claims. A total of 95 Republican delegates are at stake in New York.

The victory boosts Trump's delegate lead against Cruz, his nearest rival, who has fared far better in more conservative Southern and rural states.

Clinton's victory over rival Bernie Sanders halts momentum that had gathered around the campaign of the US senator from Vermont, who won eight of the nine primaries before New York.

Clinton had 57.5 per cent of the vote to 42.5 per cent for Sanders with 90 per cent counted.

The former secretary of state will claim a sizeable majority of the 291 Democratic delegates at stake in New York.

"Tonight the race for Democratic nomination is in the home stretch, and victory is in sight," Clinton told cheering supporters in New York's Brooklyn borough.

"It's humbling that you trust me with the awesome responsibility that awaits our next president."

She said accused both Trump and Cruz by name of "pushing a vision for America that is divisive and frankly dangerous."

She reached out to Sanders supporters: "There is much more that unites us than divides us."

Like Trump, both Clinton and Sanders have close ties to New York. Prior to the primary all three had emphasized their familiarity with the state: Sanders and Trump were born in New York City, and New Yorkers twice elected Clinton to the US Senate.

In Brooklyn's Williamsburg neighbourhood, trapeze artist Jesse Carretta, 39, said he voted for Sanders: "His ideology, his stump speeches, everything he says is far more in line with my political views. He's clearly far to the left of Clinton."

Technology consultant Jen Fish, 37, preferred Clinton for her past work first lady and secretary of state: "I liked a lot of Sanders' ideas, but I think she has more experience, especially on foreign policy."

Ron Hansen, 54, a retired corrections officer and lifelong New Yorker, voted for Trump in the Republican primary.

"I'm pissed off at politicians," Hansen said. "He's not a politician, he's a businessman."

The vote was marred by irregularities, including the improper removal of Democratic voters from voter rolls, reported in New York City, prompting the New York City comptroller to announce an audit of the Board of Elections.

The comptroller said in a statement that the Board of Elections had confirmed that more than 125,000 Democratic voters in Brooklyn had been dropped since November.

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