Fuel cells have already been developed but the technology does not yet exist to produce them on a cost-effective, commercial basis - the key to widespread use that would help fight global warming.

"Hyrodgen and fuel cells are not around the corner," IEA Executive Director Claude Mandil told a news conference.

"Huge public and private investment and research and development efforts are required to meet the expectation of a new generation of vehicles with nearly zero emissions and to reduce oil dependence in transport," he said.

The IEA's call for more investment in emerging fuels coincided with a United Nations conference in Canada that is trying to step up the fight against global warming by pushing for limits on emissions of greenhouse gases.

Fuel cells use a chemical reaction to produce electricity from hydrogen. The process emits only small amounts of carbon dioxide, the main greenhouse gas blamed for global warming.

Fuel cell designs with long enough life spans and the ability to power cars over long enough distances before refuelling will need to emerge before a new breed of hydrogen cars hits the showrooms.

The IEA said trillions of dollars needed to be spent in the coming decades to develop widespread use of hydrogen and fuel cells across the world.

Last year, government spending on research and development into hydrogen and fuel cells amounted to a combined $1 billion in the 26 industrialised countries that belong to the IEA.

General Motors said in October it was committed to building low-pollution cars which run on hydrogen but that cost and design challenges meant commercial production was about a decade away.