US Vice President Kamala Harris' election campaign has raised $200 million and signed up 170,000 new volunteers in the week since she became a presidential candidate.

US President Joe Biden ended his re-election bid on Sunday last week and endorsed Harris for the November vote against Republican former President Donald Trump.

"In the week since we started, Kamala Harris has raised $200 million. 66 percent of that is from new donors. We have signed up 170,000 new volunteers," Harris' deputy campaign manager, Rob Flaherty, posted on X.

Harris has secured support from most delegates to the Democratic National Convention, likely ensuring she will become the party's nominee for president next month.

Harris, the first Black woman and Asian American to serve as vice president, pulled in her first $100 million in the 36 hours after Biden's announcement, her office said.

Harris' takeover has re-energised a campaign that had faltered badly amid Democrats' doubts about Biden's chances of defeating Trump or his ability to continue to govern had he won.

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Mitch Landrieu, a campaign co-chair, said on MSNBC that Harris "had one of the best weeks that we've seen in politics in the last 50 years".