According to Hong Feng, deputy mayor of Beijing, the capital can be included in the third group of cities.

Zhou said the recent smog across the country affected 600 million people in 17 provinces, autonomous regions and cities that cover about one-fourth of the country.

To get the problem under control in the long run, Zhou said the ministry is considering launching a working group to tackle pollution.

In a plan released by the ministry in early December, 13 key regions were highlighted to combat PM2.5.

"Those regions are the most heavily polluted and densely populated," said Zhao Hualin, director of the ministry's pollution prevention department. The annual mean PM2.5 level will be reduced by 5 percent by 2015 in 10 of the key regions according to the plan.

For the other three - the Beijing-Tianjin-Hebei industrial cluster, Yangtze River Delta Economic Zone and the Pearl River Delta Economic Zone - the reduction target is set higher at 6 percent.

"More than 100 days per year, these three regions are enveloped in haze," said Zhao.

Experts have been worrying about the feasibility of cooperation among different cities within a region, calling for detailed legal explanations.

As the Chinese Lunar New Year draws near, Zhou targeted firecrackers and fireworks.

"PM2.5 readings on New Year's Day in 2012 reached as high as 1050 (mcg per cu m)," he said. Even during the recent pollution in mid-January the highest level of PM2.5 was 900 mcg per cu m.

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