BEIJING: China's environment minister said on Thursday that emissions of four major pollutants dropped last year and should fall by a similar level this year, but admitted the country faced a tough task in trying to end chronic air pollution.

This winter's pollution, especially in northern China, has been so severe that even usually pliant state media has criticised government inaction, partly because it can't be hidden from the public unlike other sensitive subjects such as high-level corruption.

But emissions of sulphur dioxide, nitrogen oxides, chemical oxygen and ammonia nitrogen all recorded on-year falls of two percent in 2012, and were expected to drop by the same degree in 2013, or even faster, state media cited Zhou Shengxian as saying.

"To cope with an air quality crisis, contingency measures will be adopted, such as suspending or limiting the production of certain vehicles and limiting emissions and car usage," the official Xinhua news agency cited him as saying.

"The ministry will also ban the operation of vehicles registered before 2005 under exhaust emissions requirements ... and efforts will be made to improve the quality of gasoline and diesel."

But Zhou said China "faces a long battle" in controlling what is known as PM2.5 intensity, which measures particulate matter in the air with a diameter of 2.5 micrometers.

Pollution levels in Beijing and many other Chinese cities regularly exceed 500 on that index. A level above 300 is considered hazardous, while the World Health Organisation recommends a daily level of no more than 20.

The ministry had set timetables for cities plagued by air pollution, the report said.

Cities with air pollution 30 percent above the national standard or higher should try to meet those standards by 2030, it added, without providing details.

Smoke from factories and heating plants, winds blowing in from the Gobi Desert and fumes from millions of vehicles can combine to blanket northern Chinese cities in a pungent shroud for days on end.

The government has promised repeatedly to resolve the problem, and in recent days has unveiled new measures, including taking 180,000 old vehicles off the road in Beijing this year and controlling the "excessive" growth of new car sales in the city.