Democratic candidate Hillary Clinton has reached the required number of delegates for her nomination, an AP tally suggests.
The count puts Hillary Clinton on 2,383 – the number needed to make her the presumptive nominee.
Hillary Clinton will become the first female nominee for a major US political party.
However, rival Bernie Sanders said Hillary Clinton had not won as she was dependent on superdelegates who could not vote until July’s party convention.
Hillary Clinton reached the threshold with a big win in Puerto Rico and a burst of last-minute support from superdelegates, AP reported.
At an appearance in Long Beach, California, shortly after the news broke, Hillary Clinton said: “We are on the brink of a historic and unprecedented moment but we still have work to do.
“We have six elections tomorrow and we’re going to fight hard for every single vote, especially right here in California.”
Voters will go to the polls for Democratic primaries on June 7 in California, Montana, New Mexico, North Dakota, South Dakota, and New Jersey.
The nominee for either party is not officially named until the parties’ respective conventions.
Bernie Sanders has vowed to stay in the race until the convention, and his campaign team said the Vermont senator would attempt to win back superdelegates who have pledged their support to Hillary Clinton.
His spokesman Michael Briggs said it was too early to call the Democratic contest.
“It is unfortunate that the media, in a rush to judgement, are ignoring the Democratic National Committee’s clear statement that it is wrong to count the votes of superdelegates before they actually vote at the convention this summer,” Michael Briggs said.
“Our job from now until the convention is to convince those superdelegates that Bernie is by far the strongest candidate against Donald Trump.”
Hillary Clinton, a former secretary of state, New York senator and First Lady, leads Bernie Sanders by three million votes, 291 pledged delegates and 523 superdelegates, according to AP’s count.
She has won 29 caucuses and primaries to his 21 victories – and an estimated 2.9 million more voters have backed her during the nominating process.
That gives Hillary Clinton a significantly greater lead over Bernie Sanders than Barack Obama had over her in 2008 – he led by 131 pledged delegates and 105 superdelegates at the point he clinched the nomination.