The Chinese government has approved 524 such clean development mechanism (CDM) projects, said Yang Hongwei, director of the Chinese government's CDM project management centre.

But only 90 projects have reached the next step of official registration by a United Nations body, a bureaucratic stamp needed to start selling carbon credits. Of those, 19 have begun operating, Yang said.

The projects that have cleared the Chinese approval process would cumulatively yield 180 million tonnes per year of cuts in carbon dioxide emissions, he estimated.

Another batch of Chinese approvals is expected in the near future, bringing the total number of projects to about 600, Yang said.

He spoke at the launch of a 2.8 million euro (US$3.8 million) European project to train Chinese firms to navigate the approval process.

A dearth of Chinese firms that can verify and validate the projects for the United Nations, as well as new types of projects in China which require the development of new methodologies, have contributed to the backlog.

"People have been concerned by the slow level of approval," said Zhang Jianyu, programme manager of Environmental Defense in China.