The business magnate says he will not enter a race he cannot win.

Michael Bloomberg, the billionaire former mayor of New York, has said he will not join the US presidential race for fear it would enable a victory by Republican candidates Donald Trump or Ted Cruz.

“That is not a risk I can take in good conscience,” he wrote on Bloomberg View, an opinion website that is part of his media empire.

Bloomberg had been considering a presidential run, according to reports last month.

Combining business-friendly policies with liberal social views he would likely have appealed to centrist voters – although overall, he had not received much interest from voters.

About 12 per cent of likely voters said they would support him in a three-way race for president with Democrat Hillary Clinton and Trump, according to a Reuters/Ipsos national poll conducted from Wednesday to Monday.

After concluding he could not win, Bloomberg said that his involvement could lead to the election of Donald Trump or Ted Cruz – something he said he “could play no part in”.

“As the race stands now, with Republicans in charge of both Houses, there is a good chance that my candidacy could lead to the election of Donald Trump or Senator Ted Cruz,” he wrote.

Bloomberg went on to accuse Trump of running “the most divisive and demagogic presidential campaign I can remember, preying on people’s prejudices and fears” and appealing to our “worst impulses.” He calls Cruz “no less extreme.”

The business tycoon says he is not yet ready to endorse any of the other candidates – although many believe he will eventually lend his support to Hillary Clinton.

Mr Trump has rallied against equality in recent weeks, telling old Fox News he would “strongly consider” a plot to overturn same-sex marriage, and telling evangelical leaders they can “trust” him to protect “traditional marriage”.

However, he has tied himself in a knot by simultaneously telling a lesbian journalist that he would “move forward on LGBT rights” – and when challenged attempted to maintain both viewpoints simultaneously.