A leading researcher said on Tuesday that Hong Kong needs to trial different types of green transport so it can better understand their potential, as well as the pitfalls of their use.

Dr Lawrence Cheung, chief innovation officer at the Hong Kong Productivity Council, was speaking on RTHK's Hong Kong Today programme, days after the SAR's first hydrogen-fuelled bus entered service. The MTR says it's also planning to trial hydrogen power in a light-rail train.

Cheung told RTHK's Janice Wong that hydrogen emits no carbon and refuelling is much faster than with electric vehicles, but challenges remain in putting the infrastructure in place for widespread use.

"Also we need to consider how the buses are being maintained and repaired," he said. "The other thing is: where the hydrogen will be coming from. I think it is a whole ecosystem of the whole transportation system that needs to be considered, and at the moment we are only at the start."

Cheung noted that one positive for hydrogen use in Hong Kong was that it could be sourced from towngas, which is widely used here. But he suggested that one alternative option, at least in the short term, was to make use of green methanol as vehicle fuel.

"Methanol, many people would think that it already contains carbon, because the chemical formula contains carbon," he said. "But for green methanol, the carbon itself would be captured itself from the atmosphere, so green methanol is carbon neutral.

"If we make use of green methanol, the modifications on the vehicles would be much less and the infrastructure would be easier to set up."

Citybus put the first hydrogen-fuelled double-decker into use on route 20 between Kai Tak and Cheung Sha Wan. The company said it planned to use hydrogen buses on Hong Kong Island when a refuelling point is set up there. It's also buying electric buses so it can compare their performance.