WASHINGTON: US Vice President Kamala Harris launched her election campaign Monday with a blistering personal attack on Donald Trump and vowed to win in November despite the "rollercoaster" of President Joe Biden's shock exit.

As she closed in on the Democratic party's nomination with the support of a slew of heavyweights and massive voter donations, Kamala lashed out at Trump in her first speech to campaign workers since Biden's announcement Sunday.

Biden, 81, meanwhile made his first public remarks for nearly a week as he recovers 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 Kamala as "the best."

"We are going to win in November," a smiling Kamala told campaign workers in her fiery speech at campaign headquarters in Wilmington, Delaware.

She said she had gone to the Wilmington office to address them personally after the "rollercoaster" of the last few days.

Turning her fire on Trump, Kamala referred to her past role as California's chief prosecutor, saying 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.

Kamala 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 dropped out on Sunday and endorsed Kamala 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 Kamala won the backing of a seemingly unassailable number of Democrats, most notably powerful former US House speaker Nancy Pelosi.

Pelosi's was the biggest yet as the influential 84-year-old said she endorsed Kamala "with immense pride and limitless optimism"

Donors have also rallied, pouring a record US$81 million into Kamala's campaign in 24 hours after Biden stood aside.

The campaign claimed the US$81 million haul since Sunday was the largest one-day haul in presidential history - and that, among the 888,000 grassroots donors, some 60 percent were making their first 2024 contribution.

In his comments, Biden's voice sounded husky as he explained his decision to step aside from the race and pledged that he would keep working on key topics, including ending the war in Gaza.

Addressing Kamala, he added: "I'm watching you kid. I love you."

In a strikingly symbolic moment on Monday morning, Kamala hosted a ceremony for college athletes at the White House on Monday while Biden remained stuck in isolation with Covid at his Delaware beach house.

"Joe Biden's legacy of accomplishment over the past three years is unmatched in modern history," Kamala said in her brief remarks on the White House South Lawn, as a light rain fell.

Biden's symptoms "have almost resolved completely," his doctor said Monday, though the White House has not yet announced any events on his schedule this week.

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 in modern US history.

The move has jolted a demoralised party that Kamala 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.

Kamala'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 Kamala posed a "threat to democracy."

Trump's running mate J.D. Vance echoed that line of attack at a rally in Ohio Monday, telling supporters that Kamala had the momentum because "elite Democrats got in a smoke-filled room and decided to throw Joe Biden overboard."

"That is not how it works. That is a threat to democracy," he said.

 -AFP