• The 77-year-old is expected to file paperwork this week for the Democratic presidential primary in Alabama.
• Former Vice-President Joe Biden, Massachusetts Senator Elizabeth Warren and Vermont Senator Bernie Sanders are the Democratic frontrunners.
Billionaire businessman Michael Bloomberg is strongly considering entering the race for the US Democratic Party's presidential nomination.
The ex-New York City mayor is concerned the current field of candidates is not good enough to beat Donald Trump in the 2020 election, his spokesman says.
The 77-year-old is expected to file paperwork this week for the Democratic presidential primary in Alabama.
A total of 17 candidates are currently vying to take on President Trump.
Former Vice-President Joe Biden, Massachusetts Senator Elizabeth Warren, and Vermont Senator Bernie Sanders are the Democratic frontrunners.
Some recent opinion polls have suggested that Ms Warren and Mr Sanders - who are regarded as to the left of Mr Biden - might lose against Republican Mr Trump if either won the party's nomination.
Mr Bloomberg's spokesman said: "We now need to finish the job and ensure that Trump is defeated. But Mike is increasingly concerned that the current field of candidates is not well-positioned to do that."
Who is Michael Bloomberg?
Mr Bloomberg was a Wall Street banker who went on to found the financial publishing empire which bears his name. A philanthropist, he has donated millions of dollars to educational, medical and other causes.
Originally a Democrat, he became a Republican to mount a successful campaign for mayor of New York City in 2001.
He went on to serve three terms as mayor until 2012, rejoining the Democratic Party only last year.
Regarded as a moderate Democrat, he has highlighted climate change as a key issue, but he had appeared to dismiss a potential run for the presidency earlier this year.
Mr Bloomberg is a large financial backer of gun-control advocacy group Everytown for Gun Safety, which he helped found in 2014.
The group, and Mr Bloomberg were seen as playing a major role in a sweeping victory for Democrats in Virginia state elections earlier this week.
They vastly outspent gun lobby group the National Rifle Association - which is based in Virginia - by pumping $2.5m (£1.94m) into the state race.