A high-speed train is discolored after making the journey from Xuzhou to Beijing, Jan 4, 2016. PHOTO: Sinaweibo China Daily/Asia News Network Jan 05, 2017 Smog blankets northeast China Open gallery More than 40 cities in China's northeast have issued pollution warnings in the past 48 hours after being blanketed by heavy smog. Open gallery Air quality index (AQI) readings at some monitoring stations in Tianjin, a port and industrial city southeast of Beijing, peaked above 400. Open gallery China's environmental watchdog issued a five-day warning on Friday about choking smog spreading across the northeast. Open gallery The authority also ordered factories to shut, recommended residents stay indoors and curbed traffic and construction work. Open gallery Pollution alerts have become increasingly common in China's northern industrial heartland, especially during winter when energy demand - much of it met by coal - skyrockets. Open gallery In addition, heavy winds force pollution from nearby provinces to the Beijing-Tianjin area where it remains suspended over the cities. Open gallery Beijing's city government ordered 1,200 factories near the Chinese capital, including a major oil refinery run by state oil giant Sinopec, to shut or cut output on Saturday. Open gallery On Saturday, 22 cities issued red alerts including top steelmaking city Tangshan in Hebei province around Beijing, and Jinan in coal-rich Shandong province. Open gallery Red alerts are issued when the AQI is forecast to exceed 200 for more than four days in succession, 300 for more than two days or 500 for at least 24 hours. Open gallery Tianjin was placed on orange alert - the second highest level - on Sunday. Open gallery In Beijing, the city's Municipal Environmental Monitoring Centre showed air quality readings of above 300 in some parts on Sunday (Dec 18) afternoon. Open gallery But the index was below 200 in most parts of the Chinese capital. Open gallery "When I went out yesterday I didn't wear a mask and my throat really hurt and I felt dizzy. It was hard to breathe through my nose," Chen Xiaochong, a hotel manager in the capital, told Reuters Open gallery Open gallery A man swims in a lake in smog during a heavily polluted day in Beijing. Open gallery The forbidden city is seen in smog during a heavily polluted day.