WILMINGTON: White House hopeful Joe Biden on Wednesday holds his highly-anticipated joint campaign debut with running mate Kamala Harris, who hopes to make history as the nation's first female and first black vice president.

The Democratic duo, unveiled Tuesday by Biden after a months-long search for his partner on the ticket, now launch the 83-day sprint to the election face-off against President Donald Trump.

The choice of Harris, a 55-year-old US senator from California and daughter of Indian and Jamaican immigrants, was kept secret until the last moment, even though she was widely perceived as the wire-to-wire frontrunner.

In footage released Wednesday, Biden is seen speaking with her by video chat, apparently at the moment he told her of his decision.

"You ready to go to work?" he asks.

"Oh my God. I am so ready to go to work," Harris replies.

Biden's VP reveal marks a crucial moment as he aims to build a broad coalition of voters to defeat Trump.

It also offers a chance to capture momentum in a campaign turned upside down by the coronavirus pandemic, which has largely confined the 77-year-old Biden to his home in Wilmington, Delaware.

Harris, a former California attorney general, is the first woman of color and first Indian American to be a presidential running mate, and personifies the diversity seen as key to building enthusiasm for the Democratic ticket.

Scheduled to appear with Biden in Wilmington at about 4:00 pm (2000 GMT), Harris will be perceived by many voters as a safe pick, a known quantity vetted during her time as a presidential candidate and tested on the campaign trail.

She is also a fierce defender of efforts to end economic inequality and racial injustice - in an election year marked by a historic reckoning on race.

She has valuable Capitol Hill experience and has shown her tenacity in holding Trump administration officials to account. And as California attorney general for six years Harris has run the largest statewide legal agency in America.

Biden has made clear he believes Harris has the policy proficiency and the governing experience needed for the White House.

"If @KamalaHarris and I are elected, we're going to inherit multiple crises, a nation divided, and a world in disarray," Biden tweeted Wednesday.

"We won't have a minute to waste. That's exactly why I picked her: She's ready to lead on day one."