Clinton, Trump triumph in New York
US networks called the race for the Republican frontrunner seconds after the polls closed in the country's fourth most populous state, signaling a crushing victory over his rivals.
"I have to say to the people that know me the best – the people of New York -- when they give us this kind of a vote it's just incredible," the 69-year-old businessman told a victory party at Trump Tower in Manhattan.
Trump, whose campaign has appalled the Republican establishment, led on 65.1 per cent to 13.7 per cent for his evangelical rival Ted Cruz and Ohio Governor John Kasich on 21.2 per cent, with 9% of the vote counted CNN said.
He told supporters his campaign was going to "get a lot more delegates than anyone projected even in their wildest imagination."
Clinton was declared the winner over Vermont Senator Bernie Sanders around 40 minutes after the polls closed.
The former first lady and New York senator had 60.5% of the vote, against 39.5% for Sanders, CNN said based on nearly half of precincts reporting.
Clinton had banked on victory in her adopted home state to stall the momentum generated by her self-styled democratic socialist rival and get a needed shot in the arm after losing seven out of the eight previous nominating contests.
It was New York's most decisive primary in decades and Trump's victory in the state, which has 95 Republican delegates in play, will bolster his quest to sew up the nomination before party grandees can swing behind another candidate at the convention in July.
While New York City is largely Democrat, Republicans in rural areas and fallen manufacturing cities upstate warmed to Trump's populist message, despite his insults towards women, Mexicans and Muslims.
A relaxed and confident-looking Clinton, 68, dressed in a colorful tunic, voted earlier yesterday with husband, former president Bill Clinton, in the leafy Chappaqua suburb they call home.
"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," she said.
The three main candidates also claimed New York as home: Trump, who has never lived anywhere else; Clinton, who was twice elected the state's US senator; and Sanders, who was raised in Brooklyn.