Yang Shuqin, a 59-year-old tai chi practitioner in Beijing, holds an iPad at the Temple of Heaven on Tuesday as the city was shrouded in heavy smog. The iPad picture shows the landmark structure during good weather. ZOU HONG/CHINA DAILY

Shenyang in Northeast China's Liaoning province had the worst air pollution among the 74 major cities in the nation, and the other two northeastern provinces - Heilongjiang and Jilin - also saw their capital cities listed in the top 10.

Read More: Things you may want to know during Beijing's red alert

The three provinces were blanketed by heavy haze in the first two weeks of November due to the start of central heating services, which consumes large quantities of coals.

The extreme readings of PM2.5 have surged to around 1,400 micrograms per cubic meter in Shenyang. The national safety level is 75.

In addition to the three cities in the northeast, the seven other worst polluted cities were in the northern region, especially from Hebei province.

Among the 11 cities in the Beijing-Tianjin-Hebei area, eight had more than 15 days with severe air pollution, including Beijing.

On Nov 30, heavy smog covered 70 cities, an area of more than 530,000 square kilometers, similar to the land area of France, it said.

The environmental watchdog said soaring coal consumption from heating plants was the major reason for the alarmingly severe smog.