Students in a primary school in Shijiazhuang, capital of Hebei province, have their physical education class on Wednesday in a gym covered with an air cleaning system. [Photo by WANG XIAO/XINHUA]

Along with the smog alerts, China also issued a red alert for fog on Tuesday, the first since the government revised the fog warning system in 2013.

On Wednesday, heavy fog had engulfed vast northern regions including Beijing, Tianjin and the provinces of Hebei, Henan and Shandong, reducing visibility to 50 meters, said Gui Hailin, senior engineer of the China Meteorological Administration.

The fog covered an area as large as 150,000 square kilometers, severely disrupting traffic, he said.

The fog was forecast to lift in some parts on Wednesday night, thanks to wind, which will also ease the heavy air pollution, he said, adding that the affected areas are forecast to have clean air beginning on Sunday night.

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