Kamala Harris waves to the crowd in Oakland, California. AP

Harris, 56, is widely seen as an obvious candidate for the Democratic Party nomination in 2024 should Biden, who will be 78 at their inauguration on Jan. 20, decide not to seek a second term. She hasn't weighed in publicly on such speculation.

Edison Research and the major U.S. television networks on Saturday projected their victory, based on unofficial final results, even though the incumbent president, Republican Donald Trump, vowed to continue fighting in courts.

A US senator from California, Harris has a track record of shattering glass ceilings. She served as San Francisco’s first female district attorney and was California's first woman of color to be elected attorney general.

Her background in criminal justice could help a Biden administration tackle the issues of racial equality and policing after the country was swept by protests this year. She is expected to be a top adviser on judicial nominations.

Harris, whose mother and father emigrated from India and Jamaica, respectively, had her sights set on becoming the first woman US president when she competed against Biden and others for their party's 2020 nomination.

She dropped out of the race last December after a campaign hurt by her wavering views on healthcare and indecision about embracing her past as a prosecutor.