WASHINGTON - First-term Democratic Senator Kamala Harris of California, a rising party star and outspoken critic of President Donald Trump's immigration policies, launched her 2020 campaign for the White House on Monday by touting her prior career as a prosecutor.

Harris, 54, the daughter of immigrants from Jamaica and India, enters the race with the potential advantage of being the Democratic candidate who looks most like the party's increasingly diverse base of young, female and minority voters.

"I have the unique experience of having been a leader in local government, state government and federal government," she said in an appearance on ABC's Good Morning America.

She timed her announcement for the US Martin Luther King Jr. Day holiday honouring the slain civil rights leader, saying he was an aspirational leader.

"We are the best of who we are when we fight to achieve these ideals," she said on ABC. "We are flawed, we are not perfect, but we are a great country when we think about the principles upon which we're founded."

The former California state attorney general has become popular with liberal activists for her tough questioning of Trump administration appointees and officials, including Supreme Court nominee Brett Kavanaugh and former Attorney General Jeff Sessions, during Senate hearings.

Her campaign will focus on reducing the high cost of living with a middle-class tax credit, pursuing immigration and criminal justice changes and a Medicare-for-all healthcare system. She has said she will reject corporate political action committee money.

Harris' campaign will be based in Baltimore, with a second office in Oakland, California. Her slogan will be "For the People," in a nod to Harris' roots as a prosecutor, aides said.

She will hold a launch rally in Oakland before the end of the month.

As one of the earliest congressional critics of President Donald Trump's immigration policies, Harris has pushed hard for a deal to protect from deportation those immigrants who came to the country illegally as children, a group known as Dreamers.

Harris is the fifth Democrat to enter what is shaping up to be a crowded battle for the nomination to challenge Trump, the likely Republican candidate.

She and other Democrats will have to navigate the party's debate about whether an establishment figure who can appeal to centrist voters or a fresh face who can energise its increasingly diverse and progressive base offers the best chance to beat Trump in 2020.

Harris, who made history in 2016 as the first black woman elected to the US Senate from California, has embraced the party's diversity ahead of a Democratic nominating campaign where minority voters and liberal activists are expected to have an outsized voice.

Reuters