City's fleet of yellow cabs to turn green by 2012

Announcing the initiative on NBC's Today Show, Mr Bloomberg said it was part of the city's long-range plan to reduce its carbon emissions by 30 per cent by 2030.

"There's an awful lot of taxi cabs on the streets of New York City obviously, so it makes a real big difference," said Mr Bloomberg, who is often touted as a potential independent US presidential candidate.

"These cars just sit there in traffic sometimes, belching fumes."

New York has just 375 hybrid taxis but, under the new timetable, 1000 will be on the road by October next year. The entire fleet will be converted within five years.

"It's a lot better for all of us," Mr Bloomberg said.

Hybrid cars generally have small fuel-efficient engines combined with an electric motor that helps the engine when accelerating.

The electric motor is powered by batteries that recharge automatically while the car is in use. The resulting fuel economy means hybrids emit much less pollution than standard petrol vehicles.

Mr Bloomberg said the hybrid taxis had proved successful over the past 18 months.