Mr Bloomberg is a billionaire Profile: Michael Bloomberg

The move has fuelled speculation that he may run as an independent candidate for the US presidency in 2008, although he insists he does not plan to stand.

Mr Bloomberg said a non-partisan approach had "worked wonders in New York". He is barred from seeking a third term as NY mayor in 2009.

A long-term Democrat, he switched parties when he ran for mayor in 2001.

Mr Bloomberg said on Tuesday: "Although my plans for the future haven't changed, I believe this brings my affiliation into alignment with how I have led and will continue to lead our city."

Slim chance

In recent speeches Mr Bloomberg has criticised partisan politics in the US, declaring it has paralysed decision making and jeopardised America's future.

HAVE YOUR SAY Mr Bloomberg's action shows political pragmatism. He is willing to wear any costume to get where he wants to go Tom Taylor, Penfield, NY, USA Send us your comments

The 65-year-old billionaire has enough money to finance a bid for the White House.

He is the founder of the media and financial data empire Bloomberg LP.

But analysts say that if he does run as an independent, he has little chance of success.

No independent has been voted into the White House in modern history.