PM2.5 density hit a peak of 206 micrograms per cubic meter at 7 pm on Monday in Kaifeng, Henan province, it said.

Chai Fahe, deputy director of the National Joint Research Center on Air Pollution Causes and Control, said weak wind from the south and high humidity in the region are to blame for the heavy smog. A stable atmosphere and a temperature inversion, which prevents the normal churn of the atmosphere, has occurred in many cities in the region.

He added that the northern parts of the country have entered the period of highest emission, as heating services officially begin on Thursday.

"Currently, emissions from industries and transportation sources in the region remain high. Kicked-up dust has yet to be well-controlled at various large construction sites," Chai said, adding that the start of the heating season will further increase emissions.