Former New York Mayor Michael Bloomberg has submitted his candidacy for the Democratic primary in Alabama ahead of the deadline, suggesting his seriousness about running for president.

Bloomberg is among the Democratic candidates who qualified for the March 3 primary in the southern state, the Democratic Party of Alabama said on its website.

Alabama has an early deadline for candidates to submit papers to qualify for the party's primary.

Earlier this year, Bloomberg said he would not run in the US presidential election, but left the door open to the possibility of running for him, in a statement on Thursday via Twitter to his political adviser.

Chancellor Howard Wolfson said Bloomberg was concerned that no one in the Democratic race could defeat incumbent US President Donald Trump in next year's presidential election.

Following the tweet, news reports said Bloomberg plans to catch up with the Alabama deadline and submit his candidacy papers before that date.

It is now confirmed that Bloomberg's name will appear on Alabama's ballot papers in next year's primary.

Trump mocked Bloomberg on Friday and said he had "no magic to do well."

"I know Michael, it's nothing," Trump told reporters outside the White House.

He believed the Bloomberg campaign would likely harm former vice president Joe Biden, the front-runner for the Democratic nomination, who is running as a moderate.

Bloomberg, the ninth richest man in the United States according to Forbes magazine, said in March that he would not run for president. But he then indicated that he would use his financial resources to support candidates and issues of concern to him, including fighting climate change.

Wolfson said the 77-year-old spent $ 100 million to support Democrats last year and this year helped them win control of the Virginia legislature.

"We now need to get the job done and ensure that Trump is defeated, but Mike is increasingly concerned that the current pool of Democratic candidates is not in a position to do so," Wolfson said, adding that Bloomberg will run on his track record as mayor of New York City and as a business-minded businessman. Charity.