China's environment is "still deteriorating", a senior official said Wednesday, as the booming nation burnt record amounts of coal and lagged behind in meeting its energy-saving goals.

Following 30 years of explosive growth, China's is on track to overtake Japan as the world's second-largest economy, but that success has made it one of the most polluted nations in the world.

"Our environmental quality is only improving in certain areas, but overall the environment is still deteriorating," Vice Minister of Environmental Protection Zhang Lijun told journalists.

Coal burning is a major culprit, providing the nation with up to 70 percent of its energy needs, but city waste and run-off from agriculture is also severely fouling the nation's water supply.

Zhang said although China was fulfilling its 2006-2010 goals of cutting sulphur dioxide and chemical oxygen demand - major causes of air and water pollution, respectively - emissions of other pollutants were rising.

Efforts to remove sulphur from coal resulted in less sulphur dioxide pollution in China last year, he said, despite the nation burning over three billion tonnes of the fossil fuel in 2010, an annual record.

Xie Zhenhua, who represented China at international climate change talks in Copenhagen in December, said 2010 would be a "decisive year" for the country in terms of meeting its energy-saving targets.

China had reduced its energy consumption per unit of gross domestic product by just over 14 percent from 2006-2009, but needed to cut consumption by about six percent in 2010 to reach its five-year target, he said.

"There is still a large gap to reach our energy saving goals - the task will be difficult," admitted Xie, the vice chairman of the National Development and Reform Commission, China's top economic planning agency.

China, the world's top emitter of greenhouse gases, pledged in Copenhagen to reduce carbon intensity - the measure of greenhouse-gas emissions per unit of gross domestic product - by 40 to 45 percent by 2020 based on 2005 levels.

That goal is not legally binding.

Beijing announced Tuesday it would back the deal sealed in the Danish capital, removing doubts that it was not fully on board.

Xie reconfirmed that decision at Wednesday's press conference.