The first prototype is scheduled to enter service next month, with trials expected to end in 2011.

"Brazil is one of five countries in the world that have mastered this technology and that has developed a hydrogen-powered bus," Sao Paulo's governor Jose Serra said presenting the plan.

As part of the trial three more hydrogen buses will be built as well as a hydrogen production facility.

The vehicles will be able to travel 300 kilometers (186 miles) on 45 kilograms (99 pounds) of hydrogen stored in the bus's nine tanks, and 40 kilometers (24 miles) more using battery power.

At the beginning of 2008 Sao Paulo, with 11 million inhabitants, had six million vehicles.

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