Hillary Clinton has won the Democratic primary in the state of California.
The news came hours after the former secretary of state clinched the Democratic White House nomination on the last major date of the 2016 primary calendar, with six states holding polls.
Mrs Clinton has taken a dramatic step toward the White House by winning primaries in four of those six states — California, New Jersey, New Mexico and South Dakota.
California, the most populous US state, was the biggest prize of all.
Newspapers marked Mrs Clinton’s achievement on their front pages, including the New York Post tabloid, which ran the headline “The First Lady” — a nod to her previous White House role.
In Australia, Prime Minister Malcolm Turnbull said it was a cause for celebration.
“I think it is a matter for celebration that a woman is about to be endorsed as the presidential candidate of one of the American parties,” he told 7.30. The primary victories effectively put an end to Mrs Clinton’s battle with challenger Bernie Sanders, the self-declared democratic socialist senator from Vermont who waged an extraordinarily successful grassroots campaign.
But Mr Sanders, ignoring the political writing on the wall, has vowed to “continue the fight”.
“Our mission is more than just defeating Donald Trump, it is transforming our country,” he declared to supporters in Santa Monica, California.
Mrs Clinton is now headed toward a colossal showdown in November with Donald Trump, the bombastic Republican flag-bearer.
“We believe that we are stronger together and the stakes in this election are high, and the choice is clear,” she said, before launching into a frontal attack on her Republican rival.
“Donald Trump is temperamentally unfit to be president and commander in chief.”
Mrs Clinton held a commanding lead over Senator Sanders even before Tuesday’s votes, having passed the magic number of 2,383 delegates required to clinch the nomination.
She must now reconcile a bruised and deeply divided party and rally it behind her in the brutal match against Mr Trump.
Mr Sanders has harnessed a tidal wave of anger at the ruling political class.
The drive for party unity is likely to receive a shot in the arm when President Barack Obama comes off the sidelines and offers his endorsement of Mrs Clinton, as soon as Wednesday.
That will not come as a surprise, but it could coax hardline “Bernie or bust” fans back into the party tent.
Mr Obama has approval ratings above 80 per cent with liberal democrats, who make up the bulk of Mr Sanders’ support.
The White House announced Mr Obama had telephoned both candidates to congratulate them on their hard-fought primary race, and said the President would meet with Mr Sanders on Thursday “at Sanders’ request” at the White House.