Less than a week after its biggest Japanese rival touted the economic and ecological benefits of hybrids, General Motors made a case of its own on Monday: only hydrogen-fuelled cars will survive in the end, Reuters reported.

As the debate heats up over what the car of the future will ultimately look like, car makers are staging a loud public relations battle to play up their strengths and justify the huge spending on developing the technologies so far, the news agency said.

Last Thursday, Japan's top car maker, Toyota, invited journalists to tour the production site of its new Prius hybrid to demonstrate how cheaply they could be built by sharing an assembly line with conventional mass-market cars, Reuters noted.

But Larry Burns, GM's vice president of research, development and planning, reportedly said zero-emission fuel cell vehicles (FCV) will eventually make petrol-electric hybrids obsolete, rejecting Toyota's view that hybrids will remain on the road even after FCVs become affordable for the average consumer.

"The race needs to be judged with a long-term view -- the goal is to get automobiles out of the environmental debate altogether," he told Reuters in an interview.

Reuters said GM has invested about $US1 billion in developing fuel cells to power electric motors in vehicles, and wants to be the first car maker to sell a million FCVs - it hopes to commercialise FCVs by 2010, one of the most optimistic targets in the industry.

Japan's Toyota and Honda became the first to put a saleable FCV on the road last year, but the cars are only on lease since they still cost millions of dollars to produce, Reuters noted.

Despite the many hurdles that remain to make FCVs commercially viable -- such as a lack of infrastructure and safety standards -- Burns told the news agency that weaning the industry off petrol would become imperative as fledgling car markets like those in China and India continue to grow.

"If you look at the growth of economies in the world - whether it be the US, Japan, Europe, or Brazil, Russia, India, China and Korea - commensurate with that is the growth in energy consumption," he reportedly said.

And with many countries relying almost 100% on foreign oil, they would eventually want vehicles that don't require any petrol, he told Reuters.

Still, GM stressed it will also offer other alternatives to conventional petrol combustion engines in the interim before FCVs take over, Reuters added.

In a week-long presentation in Tokyo with its Japanese affiliates that started on Monday, the GM group will showcase other cutting-edge technology such as truck maker Isuzu Motors' clean diesel engines and Fuji Heavy Industries' research into next-generation car batteries.

GM, which also has a capital alliance with mini-vehicle maker Suzuki while South Korea's Daewoo Motor plans to begin selling its first petrol-electric hybrid cars next year, Reuters said.