The severe smog blanketing northern regions, which covered more than 750,000 square kilometers by Saturday, worsened in several cities on Sunday, although officials have insisted that tough measures to reduce the pollution have been effective.

Air quality index readings in Beijing, Tianjin and cities in Hebei, Shandong, Shanxi and Henan provinces began to rise on Friday.

The worst levels over the weekend were recorded in Shijiazhuang, the capital of Hebei, where five monitoring stations recorded an AQI of 500, the most hazardous level, as of 4 pm on Sunday.