In a report on the implementation of the Air Pollution Prevention and Control Action Plan, theChinese Academy of Engineering (CAE) said although air quality in Chinese cities have improved in general, the situation is still severe.

Air quality has improved in Beijing, one of the most polluted cities in the world, in recent months after highly polluted days until last year as the capital moved out most of the highly polluting industries.

But the main challenge comes when the highly polluted haze returns in winter with high count of PM 2.5 the smallest and deadliest form of airborne particulate matter envelope the city.

Issued in September 2013, the Action Plan was created by China's central cabinet setting a number of key targets, such as building monitoring stations for PM 2.5 in all prefecture-level cities by 2015 and cutting coal consumption to 65 per cent of total energy consumption by 2017.

The CAE said in the report that PM 2.5, PM 10, nitrogen dioxide, sulfur dioxide and other pollutants have dropped year-on-year in all cities, and the number of days with heavy air pollution dropped in most cities.

However, winter air pollution is serious, and ozone pollution is emerging in some areas, the report said, adding that annual average density of PM 10 in seven provincial regions has risen.

Beijing faces a great challenge if it wants to achieve the goal for annual average PM 2.5 density to drop to 60 micrograms by 2017. Only through extraordinary measures can the target be achieved, the report said.

The report suggested that pollution treatment in southern suburbs of Beijing be strengthened, along with tougher measures in autumn and winter and strict control of diesel emissions.