BEIJING (REUTERS) - China's carbon trading scheme is still facing problems and needs further improvements, a senior climate official told reporters on Tuesday (Oct 31), as the country tries to meet its commitment to launch nationwide trading this year.

Li Gao, an official with the climate change department of China's state planner, the National Development and Reform Commission, said at a briefing in Beijing that establishing a national emissions trading system was "complex" and involved constant testing and continuous adjustments.

As part of its pledges made ahead of the Paris climate accord in 2015, China said it would set up a nationwide emissions trading scheme (ETS) in the first half of this year, but the launch has been delayed amid concerns about unreliable data.

China is already the world's biggest source of climate-warming greenhouse gases and it has pledged to bring them to a peak by around 2030 by promoting cleaner energy use and emissions trading.

Its nationwide ETS is expected to become the world's biggest once it goes into operation, overtaking the European Union's.

China had already traded an accumulated total of 197 million tonnes of carbon dioxide with a total value of 4.5 billion yuan (S$922.9 million) on its seven pilot carbon exchanges by the end of September, Li said.

"In the course of these pilot projects we gained good experiences and discovered some problems which are of great value to our efforts to launch the national scheme," he said.

Li didn't say when China would be in a position to launch the national scheme, or whether an announcement would be made during global climate talks in Bonn, beginning next week.

Xie Zhenhua, China's top climate official, told reporters at the briefing that the country remains "100 per cent" committed to fulfilling its climate pledges, despite a decision from the United States to pull out of the Paris accord earlier this year.

He said China still hoped to cooperate on issues like clean energy, noting that on a state level, the US was still making strong progress.

Separately, China also said on Tuesday that it will stop selling diesel with sulphur content higher than 10 parts per millions (ppm), usually used by tractors and ships, from Nov 1.

The move by the National Development & Reform Commission was the latest step by Beijing to clean up the nation's air.

It comes after the government banned sales of diesel with more than 50 ppm of sulphur in July.