US Vice President Kamala Harris has clarified her resolve to confront Republican nominee Donald Trump and win the November presidential election.

Harris delivered a speech to staff at the Democratic campaign headquarters in the eastern state of Delaware on Monday.

President Joe Biden announced his withdrawal from the presidential race on Sunday, and said he would back Harris as the Democratic nominee.

Harris said, "It is my great honor to have Joe's endorsement in this race, and it is my intention to go out and earn this nomination and to win."

She said Trump "wants to take our country back to a time before many of our fellow Americans had full freedoms and rights."

Harris expressed her resolve to win the November election, saying that the Democrats "believe in a future where every person has an opportunity."