Four international bodies on Wednesday called on governments and car makers to halve global vehicle emissions by 2050 as the auto industry insisted it was serious about producing greener vehicles.

The UN Environment Programme (UNEP), International Energy Agency, International Transport Forum and motoring's FIA Foundation, in a statement at the Geneva Auto Show, urged that the fuel economy target be considered part of economic aid for the industry.

UNEP executive director Achim Steiner told AFP in Geneva: "I think there area number of companies here who will now bet on a quantum leaps in energy efficiency.

"But a lot will depend on whether the consumer will be punished for buying fuel efficency by having to pay more for it," he added, suggesting that the industry had dragged its feet for years.

Most of the 120 new or modified cars launched on preview days ahead of the show's opening on Thursday offered fuel-saving or lower emissions features, as struggling auto makers seek to reverse plunging demand.

Volkswagen chairman Martin Winterkorn claimed the trend was not a passing fad and that "ecological demand" could save car makers from the brunt of the economic crisis.

"The future is green," he declared as the company launched a new sub-compact Polo, claiming eight percent less weight, more economy and lower emissions.

Hybrids, combining petrol or diesel engines and electric power, were more widespread in Geneva, while engines were generally getting smaller, more economical and more plug-in electric vehicles emerged on the stands.

With wider use of those existing technologies, six billion barrels of oil a year could easily be saved by 2050 despite an expected trebling of the world car fleet, according to an initiative launched by the four agencies.

Luxury car maker Bentley unveiled a powerful new sports version of its coupe, but engineered for "flexfuel," allowing the option of a tankful of petrol or of biofuels that can reduce carbon dioxide emissions by 70 percent, according to the maker.

"Everyone will have to do something," said communications director James Rosenthal, underlining that car makers will soon "no longer be able to rely on oil."

The surge in oil prices up to 147 dollars a barrel last year and the resulting impact on the motorist's pocket helped spur the trend, since fuel economy generally equates with lower carbon emissions.

But political pressure also counted.

After years of negotiations, the European Union last year adopted tougher, compulsory 130-gramme-per-kilometre average emissions cap for new car ranges from 2012, and the industry is scrambling to meet that target.

Peugeot chief executive Jean-Philippe Collin pointed to a combination of ways to achieve "environmental positioning."

"There's not just one single technology, there's electric, diesel, petrol, diesel hybrid, and micro-hybrids," he explained.

General Motors unveiled the Opel Ampera in Geneva, a saloon car powered by by an electric motor that can be charged by a small petrol engine or plugged into a household socket.

It could produce zero emissions or about half the usual amount of a petrol- or diesel-fuelled equivalent.

Opel hopes to put the car on sale in 2010, but GM Europe president Carl Peter Forster underlined that some everyday practical obstacles could stifle its subsequent progress.

"Its success in the market will be equally dependent on governments ... putting in place comprehensive policy frameworks that send complementary signals to electricity providers and consumers," Forster said.

Among the needs are revised building codes to allow plug-in garages, daytime charging rates for electricity, and an adequate infrastructure of sockets.