US voters are voting in six states for the last major battle of the Democratic primary season. Sanders' supporters hope to win heavyweight California, despite the reports of Clinton clinching the nomination.
Presidential hopefuls Bernie Sanders and Hillary Clinton faced off in New Jersey, Montana, North Dakota, South Dakota, New Mexico and California, as the race for the Democratic Party nominee entered its final stages on Tuesday.
Going into the vote, Vermont Senator Sanders has a total off 1,569 delegates backing him, including 48 superdelegates whose choice is not dependent on the voting results.
His rival Clinton, however, had the support of 571 superdelegates for the total of 2,383 delegate votes, according to the count published by the AP news agency. This number is enough to make Clinton the nominee at the Democratic Party convention in July.
On the Republican side, US billionaire Donald Trump reached the number of delegates needed in late May.
California at stake
The Clinton campaign urged their supporters to come out and vote, despite the news of ex-Secretary of State passing the delegate threshold.
At the same time, Sanders spokesman Michael Briggs called the AP count a "rush to judgment," pointing towards the convention on July 25 when the votes are officially cast.
"Secretary Clinton does not have and will not have the requisite number of pledged delegates to secure the nomination," Briggs said.
Polls predict a tight race between the rivals in California, with 546 delegates at stake. However, even a close victory in California would not be enough for Sanders to catch up, as the loser would also be awarded a number of delegates according to the vote.
'Berners' hard to convert
The firebrand Sanders has repeatedly pledged to stay in the race until the end. The only remaining primary contest after Tuesday, is a vote in Washington DC in a week's time.
If the party delegates support Clinton in July, she will become the first woman in US history to become a major political party's presidential nominee. Even so, she would face a tough battle to secure the votes from the Sanders camp, as many of his supporters accuse her of duplicity and corruption.
Last month, 41 percent of Bernie Sanders' supporters said they would support Clinton versus Trump, down from 50 percent in April.
Sanders reportedly said he would do "everything" to ensure Donald Trump does not become the president, and pledged to keep the Republicans out of the White House even without the nomination.