(CNN) — Schools, major roads and an airport remained closed Tuesday, as a thick cloud of filthy smog smothered the northeastern city of Harbin.
Meteorologists in the city, which is famous for its annual ice festival. issued a red alert for fog at 5 a.m. Tuesday, with visibility in some central areas of the city down to less than 20 meters (65 feet), the state-run Xinhua news agency reported.
Video from China's state-run CCTV showed some people obscured by smog even just steps away wearing masks over their mouths as they walked in the province. Some drivers who braved the roads flashed hazard lights.
Kindergartens, primary and junior middle schools were ordered to suspend classes for a second day, while Harbin Taiping International Airport remained closed with 250 flights canceled on Monday alone, according to Chinese state media.
Pollution levels remained far above international standards, as the city's monitoring stations on Tuesday showed that concentrations of PM2.5 the tiny airborne particles considered most harmful to health were more than 30 times the World Health Organization's recommended standard, the state-run China Daily reported.
Government officials blamed the smog on a lack of wind and farmers burning crop stalk after their autumn harvest, though the city's coal-burning heat system, which was recently started, is also a likely factor. Harbin's environmental bureau has also conducted checks on factories known to discharge pollutants, the China Daily report added.
Fang Lijuan, the city's chief meteorologist, said it is very rare for the city to suffer such extreme conditions.
"There has been no strong wind and the level of humidity is high," she said, in quotes carried by China Daily.
Residents of this city of 10 million people were also surprised by the thick smog.
"The pollution is indeed very bad, we can only see things within 100 meters, and yesterday it was 20-30 meters. We can smell the smoke in the air," one man, who identified himself as Mr. Ren, told CNN.
"The smog started about four days ago ... I heard all face masks in Harbin are sold out. People are very angry about this and there is a lot of discussion over the Internet.
"The main reason is Harbin started its heating and the main resource is coal. Every year at this time, the air quality is bad -- but this year is especially polluted."