Even while showing off their new-found clean and green credentials, carmakers filled hall after hall in Frankfurt with powerful, tyre-squealing sports cars boasting up to 530 horsepower, or giant gas-guzzling SUVs.

After long resistance to the debate over climate change, carmakers have shifted into overdrive, insisting they have long been working on low-emission cars and are not bowing to political pressure to reduce greenhouse gases.

In any event, some serious low-emission and even zero-emission cars shown in Frankfurt are in the pipeline or about to hit the market.

"Many of you have doubtless asked yourselves 'How green is this Motor Show?'," DaimlerChrysler Chief Executive Dieter Zetsche said as he presented 19 "clean today and clean tomorrow" cars.

"We have been focusing on this issue for some time."

Zetsche, whose powerful premium Mercedes cars strike fear into other motorists as they zip down German motorways at speeds above 200 kph, said the new vehicles were just "the latest stage in our journey towards an emissions-free future".

One clear highlight was news on Tuesday that Mercedes-Benz will begin limited serial production within three years of a small car powered by a zero-emissions hydrogen fuel cell.

Fuel cells use the interaction between hydrogen and oxygen to generate electricity that powers the car while emitting only water, but they have not yet become commercially viable.

Mercedes was also proud of its new DiesOtto engines, which combine the high torque and low fuel consumption of a diesel engine with the power and low emissions of a petrol engine.

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Ford's Volvo introduced the Volvo ReCharge Concept, a plug-in hybrid for its C30 model that can be charged up from an ordinary outlet and has a range per charge of 100 kilometres.

Toyota, whose Prius hybrid has been out for 10 years, announced a partnership with French utility EDF to set up a network of plug-in points for recharging batteries.

Stung by criticism even from German political leaders that they were asleep at the wheel and failed to match Toyota and Honda in producing hybrid petrol-electric engines, German companies are eager to make up lost ground.

"European carmakers are taking up the hybrid system to a greater extent than we had imagined," Toyota President Katsuaki Watanabe said, calling this "pleasant news" because large-scale production will help address environmental and energy issues.

BMW presented a hybrid sports activity vehicle Concept X6 (SAV) due out in 2009 that it said will slash emissions.

"We've been working on this for the last five years, long before it became an issue for the media, politicians and the public," CEO Norbert Reithofer said.

Volkswagen drew crowds of journalists around a new concept car model called simply "Up!" -- a rear-engine, three-door four-seat vehicle that sips just three 3 litres (0.7925 US gallons) of fuel per 100 km (62 miles).

General Motors' Opel unit presented the "Flextreme" electric concept car it hopes to bring out in 2010.

Opting for an electric car rather than a more expensive hybrid, Opel said the battery-powered car can hit up to 160 kph and its lithium-ion battery charged by plugging into a socket.

But environmental groups in German were sceptical.

"When it comes to camouflage, tricks and deceit, the German carmakers are world champions," said Werner Reh, traffic expert at Germany's BUND environmental group.

"Instead of incorporating available fuel savings technology in their mass production, they're trying to refashion their image as environmentally friendly with a massive campaign."

Juergen Resch, head of the DUH environmental group, added his doubts about whether there had been a real change of heart.