(CNN) -- Hazardous smog was covering Beijing on Tuesday, reducing visibility to less than 200 meters (200 yards) in parts of Chinese capital while forcing the cancellation of airline flights and the closure of highways, Chinese state media reported.
The U.S. Embassy in Beijing reported that at 8 p.m. local time Tuesday air quality had been at hazardous levels for the past 24 hours, meaning that "everyone should avoid all physical activity outdoors; people with heart or lung disease, older adults, and children should remain indoors and keep activity levels low," according to the embassy's website.
Citizens were fed up with the hazardous air. The latest blanket of smog, which began to cover the eastern China area on Monday, is the fourth to menace the area since the beginning of the year.
"The air pollution is terrible. It's bad for citizens' health. They need to sort it out, the department responsible needs to sort out the environment," Beijing resident Zhang Shuquing was quoted as saying by China Radio International.
"I'm standing outside my office building but am unable to see its top," one office worker wrote on Sina Weibo, China's version of Twitter, according to a report from the state-run Xinhua news service.
The air is so bad that some pedestrians in Beijing have abandoned ordinary face masks for gas masks and respirators, Xinhua reported.
A Beijing pediatric hospital says it has treated a record 9,000 children this month for respiratory illnesses, most of which doctors and patients blame on the smog, Xinhua reported.
Relief may come by Wednesday night, when snow and rain moving into the region should clear the air, Chinese weather authorities said in a report from China Daily.