The move is an about-face for Bloomberg, 77, who said in March he would not make a 2020 run for the White House.

Michael Bloomberg announced on Sunday he is running for president, joining the crowded field of Democrats seeking to take on his fellow New York billionaire, President Donald Trump.

“I’m running for president to defeat Donald Trump and rebuild America,” Bloomberg, 77, said on his webpage as a $30m Bloomberg ad campaign hit US airwaves.

The announcement ended speculation about the intentions of Bloomberg, who for weeks has been filing paperwork to be eligible as a candidate in primary voting and registered with the Federal Election Commission.

The move was an about-face for Bloomberg who said in March he would not make a 2020 run for the White House.

“We cannot afford four more years of President Trump’s reckless and unethical actions,” the former New York mayor said.

“He represents an existential threat to our country and our values. If he wins another term in office, we may never recover from the damage.”

With a personal fortune of $50bn, Bloomberg will shake up the open race, with 17 candidates already vying to be the Democratic nominee to take on Trump next year.

Former Vice President Joe Biden leads the race ahead of left-wingers Elizabeth Warren and Bernie Sanders, with moderate Pete Buttigieg in fourth place, according to national polls.

‘Disgusted’

Even before the announcement was made, Democratic rivals such as Sanders pounced on Bloomberg’s plans to rely on his personal fortune.

“I’m disgusted by the idea that Michael Bloomberg or any billionaire thinks they can circumvent the political process and spend tens of millions of dollars to buy elections,” he tweeted on Friday.

I’m disgusted by the idea that Michael Bloomberg or any billionaire thinks they can circumvent the political process and spend tens of millions of dollars to buy elections. If you can’t build grassroots support for your candidacy, you have no business running for president. https://t.co/jyIBVXUToj — Bernie Sanders (@BernieSanders) November 22, 2019

Warren, another leading progressive candidate, also slammed Bloomberg on Saturday for trying to buy the presidency.

“I understand that rich people are going to have more shoes than the rest of us, they’re going to have more cars than the rest of us, they’re going to have more houses,” she said after a campaign stop in Manchester, New Hampshire.

“But they don’t get a bigger share of democracy, especially in a Democratic primary. We need to be doing the face-to-face work that lifts every voice.”

Dubious record on race

Before Bloomberg’s presidential announcement, the mayors of Columbia, South Carolina, and Louisville, Kentucky, endorsed him.

Despite that show of support from two local black leaders, Bloomberg may have trouble building a multiracial coalition early on given his turbulent record on race relations in New York City.

He angered many minority voters during his 12 years in the mayor’s office for embracing and defending the controversial “stop-and-frisk” police strategy, despite its disproportionate effect on people of colour.

Facing an African American congregation this month in Brooklyn, Bloomberg apologised and acknowledged it often led to the detention of minorities.

The apology was received sceptically by many prominent activists who noted it was made as he was taking steps to enter the presidential race.