China's National Meteorological Center has issued an orange alert for smog.
The haze covers large areas of China's north, east and center parts, including Hebei, Henan, Shandong, Jiangsu and Hubei provinces as well as Beijing and Tianjin. The heavy smog cuts visibility in affected areas to less than 200 meters, and less than 50 meters in some areas.
Due to low visibility, Tianjin has closed all of the city's 19 highways. The smog is estimated to last until Saturday, when cold air will dissipate it. Roughly 50 cities in northern and eastern China have issued air pollution alerts in the most recent bout of smog.
China has a four-tier warning system, with red as the most severe, followed by orange, yellow and blue.