WASHINGTON (AFP) - A prominent Republican activist and fund-raiser says she will back Democrat Hillary Clinton for president and give money to her campaign to stop her party's nominee Donald Trump, repudiating him as a dangerous demagogue.

"I will vote for Hillary, I will talk to my Republican friends about helping her, and I will donate to her campaign and try to raise money for her," Meg Whitman told The New York Times Tuesday.

The billionaire Whitman is CEO of Hewlett Packard Enterprise and used to be chief executive of eBay. Whitman funded her own, ultimately failed campaign to be elected governor of California in 2010.

Whitman told the Times that Trump is a "dishonest demagogue" and that electing him to the White House would lead the United States "on a very dangerous journey".

Whitman said she stood by remarks earlier this year in which she compared Trump to Hitler and Mussolini, and said dictators often come to power by democratic means.

"Time and again history has shown that when demagogues have gotten power or come close to getting power, it usually does not end well," Whitman said.

She also disclosed that Clinton had reached out to her about a month ago in a telephone call.

Whitman said she is even willing to campaign for the former secretary of state.

Whitman will donate an amount in the "mid-six figures" to the Clinton campaign, the Times said, quoting an aide to her.

Whitman was a top fund-raiser for Mitt Romney's 2008 presidential campaign and chaired New Jersey governor Chris Christie's finance team this year until he pulled out of the race.

When Christie endorsed Trump, Whitman accused the governor of an astonishing display of political opportunism, the Times said.