California senator Kamala Harris has launched her presidential campaign for 2020, adding to a crowded Democratic field dominated by a new generation of women and minority candidates.

The 54-year-old former prosecutor announced her bid for the White House on Monday in an appearance on ABC's Good Morning America programme, saying "The future of our country depends on you and millions of others lifting our voices to fight for our American values. That's why I'm running for president of the United States."

She is the fifth Democrat to enter what is shaping up to be a fierce battle to challenge President Donald Trump in the 2020 election.

Senators Kirsten Gillibrand, Elizabeth Warren have already announced their campaigns, along with congresswoman Tulsi Gabbard, former San Antonio mayor Julian Castro and John Delaney, a Democratic Congressman from Maryland.

Former Vice President Joe Biden and Bernie Sanders, who ran for the nomination in 2016, are also expected to throw their hat into the ring in coming weeks.