It's a big day in the US presidential primary race. The campaigns of both parties' respective leaders have been sputtering lately, but both Hillary Clinton and Donald Trump are hoping for decisive wins in New York's delegate-rich primary.

Clinton, 68, voted with her husband, former president Bill Clinton, in their suburban hometown of Chappaqua, greeting well wishers at the polling station.

"I had a great time going around the city in the last couple of days just seeing a lot of old friends, meeting new people," Clinton said. "Everybody please come out and vote before 9:00 pm tonight. That would be terrific."

Trump, 69, cast his ballot in Manhattan.

"It was just a great honor and I think it's a great honor for New York," he said after voting in a synagogue, and reiterating his campaign slogan. "We're going to make America great again."

Both candidates have double digit leads going into today's vote but both are in need of convincing victories to minimize emerging doubts about their respective candidacies.

Clinton leads the Democrats

On the Democratic side, Clinton is up by 12 points in New York over her challenger, Vermont Senator Bernie Sanders, 74. There are 291 delegates up for grabs, and Clinton has a commanding lead in the delegate race with 1,791 compared to 1,115 for Sanders. Those numbers include so-called "superdelegates" - elected officials and party functionaries that have pledged support to a candidate though they could change their loyalties at the summer convention.

The first candidate to collect 2,383 delegates wins the party's presidential nomination. But Sanders, who was born and raised in New York City, has won seven of the last eight nominating contests, suggesting momentum is on his side after starting the campaign as a relative unknown.

A sizable win for Clinton, who was twice elected to the US Senate from New York, would greatly diminish any chance Sanders has of capturing the nomination.

Trump leads the GOP

On the Republican side, Trump has a 30-point lead in his home state where he is battling for the 95 delegates up for grabs. He currently has 744 delegates, while Texas Senator Ted Cruz has 559 and Ohio Governor John Kasich has144.

The magic number for clinching the Republican presidential nomination is 1,237 delegates. Like Clinton, Trump has a commanding lead in the Republican race. But the billionaire businessman and reality TV show figure has run a campaign that has upended the Republican political establishment.

Should Trump fail to win the 1,237 delegates outright during the primary campaign, he would face considerable opposition from the party establishment at the Republican convention - where a candidate is formally nominated to represent the party in November's general election.

bik/se (AFP, Reuters, AP)