Thick smog virtually shut down a Chinese city of 11 million today, with schools and the airport both being closed. View this photo on Instagram instagram.com Harbin, the capital of the Heilongjiang province, is said to have visibility of less than half a football field. View this photo on Instagram instagram.com According to Reuters, "An index measuring PM2.5, or particulate matter with a diameter of 2.5 micrometers (PM2.5), reached a reading of 1,000 in some parts of Harbin." View this photo on Instagram instagram.com A level above 300 is considered hazardous, but the World Heath Organization recommends daily levels of no more than 20. View this photo on Instagram instagram.com Local media reported that heavy smog affected most of the major cities in northeastern China on Monday morning. Sheng Li / Reuters A before-and-after photo taken in Shenyang in Liaoning province on Oct. 11 (bottom) and Oct. 21. Harbin before the smog: aphotostory/aphotostory / Getty Images A building by the Songhua River in Harbin. And after: China Stringer Network / Reuters A woman wearing a mask checked her cell phone in Harbin. View this photo on Instagram instagram.com The Xinhua news agency blamed the emergency on many turning their heat on for the first time that season. China Daily / Reuters A traffic policeman signaled to drivers. The smog is expected to continue for 24 hours. Sheng Li / Reuters A statue of China's late Chairman Mao Zedong.