The 15-million-Hong-Kong-dollar (US dollars 1.9 million) scheme included the development of a small hydrogen manufacturing facility and a prototype vehicle but neither was put into operation.

Green Island Cement scrapped the scheme because the Hong Kong economy was driven by fossil fuels and there was no reliable source of renewable energy to drive the hydrogen conversion process.

The Environmental Protection Department said it was supportive of the trial and had formed an interdepartmental taskforce to speed the safety and environmental assessment.

The risk assessment study was started, but terminated before completion, a department spokesman said.

"We have subsequently informed the proponent of the major outstanding risk issues that need to be addressed," he said. "In case they are interested in reviving the project again, these issues can be addressed to enable the project to proceed as quickly as possible."