Washington: US Vice-President Kamala Harris has hit out at her Republican rival Donald Trump in the first rally of her presidential campaign, portraying the election as a choice for the American people between a former prosecutor and a convicted felon.

Harris told supporters in the battleground state of Wisconsin on Tuesday that she will spend the coming weeks to unite the party ahead of the Democratic National Convention next month and her showdown with former president Trump in the November 5 presidential election.

Speaking about her record as a tough prosecutor in California, Harris, 59, said she took on perpetrators of all kinds: Predators who abused women; fraudsters who ripped off consumers; and cheaters who broke the rules for their own gain.

So hear me when I say, I know Donald Trump's type, Harris said, a day after she secured the support of a majority of Democratic delegates, paving the way for her to become the party's presidential nominee.

Trump, 78, became the first former president to be convicted of a crime when a New York jury found him guilty in May of 34 felony counts involving hush money payments to a former porn star with whom he allegedly had an extramarital affair.

"In this campaign, I promise you, I will proudly put my record against his any day of the week," Harris, the daughter of a Jamaican father and an Indian mother, said.

President Joe Biden, 81, announced on Sunday that he was withdrawing from the race and endorsed Harris as the Democratic Party's nominee, amid mounting pressure from top Democrats and donors following his disastrous debate against Trump last month.

Harris noted that less than two days after Biden exited the race and endorsed his vice president, she had amassed enough support from the delegates to become the party's presumptive nominee. She also nodded at the critical role Wisconsin will play in the race for 270 electoral college votes.

The path to the White House goes through Wisconsin. And to win in Wisconsin, we are counting on you, right here in Milwaukee. And you helped us win in 2020. And in 2024, we will win again, she said.

Political fundraisers are saying that they have seen a breathtaking financial turnaround for Democrats since Biden's withdrawal effectively ended a donor blockade in the aftermath of his poor debate performance last month.

Harris' campaign said it had collected a staggering USD 100 million between Sunday and Monday evening across all its fundraising committees far surpassing the USD 53 million that Trump's political operation touted raising after his May conviction in a Manhattan business fraud case. More than 1.1 million donors have contributed with 62 per cent of them first-time givers this cycle, Harris' campaign said.