Washington: US Vice President Kamala Harris appeared poised to clinch her party's presidential nomination after receiving support from enough Democratic delegates Monday, as she launched a blistering campaign against Donald Trump.

The formal nomination process for a US presidential candidate occurs when delegates from across the United States gather to officially anoint a nominee chosen by voters during the primaries.

But when President Joe Biden dropped out of the race on Sunday, the fate of those delegates, who had been slated to vote for him, came into question.

With the support of a slew of Democratic heavyweights, including Biden himself, and massive voter donations, Harris quickly closed in as the Democratic party's heir apparent, and delegates began falling in line to pledge their support.

"Tonight, I am proud to have secured the broad support needed to become our party's nominee," Harris wrote in a statement, after US media reported she had sailed past the number of delegates needed - 1,976 out of nearly 4,000 - in order to decisively secure the Democratic presidential nomination during voting in the coming weeks.

The news came after Harris, in her first speech to campaign workers since Biden's announcement, lashed out at Republican nominee Trump on Monday at campaign headquarters in Wilmington, Delaware.

Telling the crowd of workers she had come to address them personally after the "rollercoaster" of the last few days, she reminded them that in her past role as California's chief prosecutor, she "took on perpetrators of all kinds."

"Predators who abused women. Fraudsters who ripped off consumers. Cheaters who broke the rules for their own gain. So hear me when I say I know Donald Trump's type," she said to applause.

"We are going to win in November," a smiling Harris told the workers.

She also pledged to focus on the politically explosive issue of abortion, after Trump praised the Supreme Court's 2022 decision to overturn the long-held federal right to the procedure.

Biden, 81, meanwhile made his first public remarks in nearly a week as he recovered from a bout of Covid.

He called in to the campaign meeting to say that dropping out - after mounting party and voter concerns over his health and mental acuity - had been the "right thing to do" and he praised Harris as "the best."

On Tuesday Harris takes her fight against Trump to Milwaukee, Wisconsin where she will hold a rally hoping to bolster her following in the critical swing state.

Biden dropped out and endorsed Harris after three weeks of intensifying pressure, triggered by a disastrous debate performance against Trump.

Aiming to become the first woman president in US history, the 59-year-old Harris won the backing of a seemingly unassailable number of Democrats.

Notably among them was powerful former US House speaker Nancy Pelosi, who said she endorsed Harris "with immense pride and limitless optimism."

Donors have also rallied behind Harris, pouring a record $81 million into her campaign in the 24 hours after Biden stood aside.

The campaign claimed the haul was the largest one-day sum in presidential history - and that, among the 888,000 grassroots donors, some 60 percent were making their first 2024 contribution.

Meanwhile, an aide to Harris said she would meet with Israeli Prime Minister Benjamin Netanyahu this week during his Washington visit - separate from Biden's own planned sit-down.

And in a strikingly symbolic moment, Harris hosted a ceremony for college athletes at the White House, with Biden scheduled to return Tuesday from Delaware where he has been isolating with Covid.

Biden's stunning withdrawal has completely upended the 2024 race, transforming a long slog between two unpopular elderly men into one of the most compelling races in modern US history.

The move has jolted a demoralized party that Harris could now unify, and could give America its first female president.

It has also hit Republicans hard, with former president Trump, 78 - now the oldest presidential nominee in US history - having to completely retool a strategy that had been built around attacking Biden over his age and physical frailty.

Harris's entry not only flips the age issue, but puts Trump - a convicted felon also found liable of sexual assault - up against a woman and former prosecutor.

And Trump has seemingly found it hard to move on from Biden.

He launched a series of invective-filled social media posts after Biden quit, mocking the president's age and saying he and Harris posed a "threat to democracy."

 - AFP