Claiming her place in history, Hillary Clinton declared victory in her bruising battle for the Democratic presidential nomination, becoming the first woman to lead a major American political party.
She immediately took aim at presumptive Republican nominee Donald Trump, telling supporters in Brooklyn, New York, that he was "temperamentally unfit" to be president.
"Tonight's victory is not about one person," Clinton said. "It belongs to generations of women and men who struggled and sacrificed and made this moment possible."
She won the Democratic primaries in New Jersey and New Mexico, with rival Bernie Sanders triumphing in the presidential caucuses in North Dakota.
Trump notched up victories in primaries in New Jersey, New Mexico, South Dakota and Montana, on an otherwise difficult day as Republican leaders recoiled at his comments about a Hispanic judge, with one senator even pulling his endorsement.
Clinton later won in South Dakota, while Trump claimed victory in California.
President Barack Obama called Clinton with congratulations on securing the delegates needed to clinch the Democratic nomination.
Clinton spoke at an emotional rally in Brooklyn, New York City, eight years to the day after she ended her first failed White House run.
As she took the stage to raucous cheers, she paused to relish the moment, flinging her arms wide and beaming broadly.
"This campaign is about making sure there are no ceilings, no limits on any of us," she said.
Clinton was biting and sarcastic as she took on Trump, accusing him of wanting to win "by stoking fear and rubbing salt in wounds - and reminding us daily just how great he is".
Trump is the only remaining candidate in the race for the Republican nomination.
In a speech at his Westchester, New York, golf course, Trump said he understands he bears "the responsibility of carrying the mantle and I will never ever let you down".
However leading Republicans united in an extraordinary denunciation of his attacks on a federal judge.
House Speaker Paul Ryan called them the "textbook definition of a racist comment" - although he stood by his endorsement of Trump's presidential run.
Trump asserted that his comments were being "misconstrued" but did not back down or apologise for saying repeatedly that US District Judge Gonzalo Curiel could not preside fairly over a case involving Trump University because of the judge's Mexican heritage.