AP says she has now reached the number of delegates she needs to make her the first ever female nominee for a major US party
Hillary Clinton has reached the number of delegates needed to clinch the Democratic presidential nomination, according to an AP count.
If their tally is right, she will become the first woman to top the ticket of a major US political party.
Reluctant to celebrate too soon, Mrs Clinton greeted the news by saying she is on the brink of a "historic, unprecedented moment".
The former Secretary of State told supporters gathered at a campaign event in Long Beach, California there was still work to do as six states, including California and New Jersey, prepare for decisive votes on Tuesday.
Replying to an AP Politics tweet declaring her nomination, she added:
According to the Associated Press count, Mrs Clinton has commitments from 2,383 delegates - the magic number needed to win the nomination.
It says she has 1,812 pledged delegates, won in primaries and caucuses, and the support of 571 party insiders, known as superdelegates.
If the count is confirmed, Mrs Clinton will go head-to-head in the presidential race against presumed Republican nominee Donald Trump.
Her rival Bernie Sanders immediately rejected the tally insisting it is too soon to declare her the official Democratic nominee as superdelegates can change their minds up until the party's convention in July.
He has pledged to work over the coming weeks to sway their vote.
"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," Sanders spokesman Michael Briggs said in a statement.
"Our job from now until the convention is to convince those superdelegates that Bernie is by far the strongest candidate against Donald Trump."
The tally comes almost eight years to the day after Hillary Clinton withdrew her first shot at becoming the Democratic presidential nominee after conceding defeat to then Senator Barack Obama.