Supporters write on themselves as they wait to enter a rally where Democratic US presidential candidate Hillary Clinton will appear to celebrate her California primary night in the Brooklyn borough of New York, US, June 7, 2016. [Photo/Agencies]

LOS ANGELES - Democrat Hillary Clinton beat rival Bernie Sanders in New Jersey's presidential nominating contest on Tuesday, Fox News projected, bolstering her lead a day after she captured the number of delegates needed to become her party's US presidential nominee.

Clinton, a former first lady, senator and US secretary of state, would be the first woman to become the presidential candidate of a major US political party.

New Jersey was one of six states holding contests on Tuesday, including the big prize of California, where Clinton is still at risk of an embarrassing loss to Sanders as she heads into a campaign against presumptive Republican nominee Donald Trump in the Nov 8 election.

Other news outlets, including MSNBC and CNN, said it was still too early to call the winner in New Jersey shortly after the polls closed.

Clinton secured enough delegates to the party's convention to win the nomination before Tuesday's voting, US media outlets reported on Monday night.

But Clinton campaign manager Robby Mook said the campaign was pushing supporters and volunteers to "stay at this" for the contests in New Jersey, Montana, North Dakota, South Dakota and New Mexico and California.

"We're on the verge of making history, and we're going to celebrate that tonight," Mook told CNN. "There's a lot of people we want to make sure turn out today. We do not want to send a message that anybody's vote doesn't count."