Hillary Clinton was poised to clinch the Democratic party nomination that will make her the first ever woman presidential nominee of a major party in the US after she convincingly defeated her rival Bernie Sanders in two primaries ahead of a crucial one in California.

The former secretary of state posted strong wins over Sanders in the island territory of Puerto Rico and the US Virgin Islands, the Press Trust of India (PTI) reported.

Clinton will have enough delegates by tomorrow when a multi-state primary vote will take place in six states including California, her close aide said.

"We think we're going to come out of Tuesday night with the delegates we need for her to be the first woman nominee on a major party ticket in the United States. So, we're looking forward to that," John Podesta, chairman of the Hillary Clinton Campaign, told Fox News.

Clinton now has 2,354 delegates - 28 short of the 2,382 she needs to bag the Democratic party's nomination.

A win in delegate-rich California is crucial for the 68-year-old former first lady in her fight against Vermont Senator Sanders, who has 1,565 delegates. California has 546 delegates to be secured.

The other states where primaries will be held are - Montana (27 delegates), New Jersey (142), North Dakota (23), New Mexico (43), and South Dakota (25)

"What we're saying is that she will have the delegates to be the nominee. We're going to do everything we can to reach out to appeal to his supporters, to appeal to his (Sanders) campaign and to him directly.

"We want to bring this party together because the country faces a major threat in Donald Trump. We hope that he will join us," Podesta said.

He exuded confidence that Clinton would be way ahead of Trump, the presumptive Republican presidential nominee, during the general elections.

"He (Trump) has consolidated the Republicans. That's led to something of a tightening of a pulse. But this has really just begun. That's why Hillary Clinton on Thursday of this week went to San Diego and really laid out a strong case about why he's unfit, why he does not meet the commander-in-chief test," he said.

"And what did she use to prove that point? Really his own words, the things he said in this campaign from being in favour of expanding and proliferating weapons of mass destruction and nuclear weapons to pulling out of NATO to offending our allies and supporting dictators around the world," Podesta said.

He argued that over the long term people are going to come to see Trump as not having the temperament to serve as president and commander-in-chief.

"The card we're going to play against Trump is that he has always been for himself. He's a self-aggrandiser at the expense of literally thousands of people," the top Clinton aide said.