Airports, schools closed as thick smog blankets Chinese city of Harbin Coughing and commuting Masking the problem Almost invisible Road block Health hazard Smog smothered Disappearing bridge Visibility in some central areas of the city down to less than 20 meters (65 feet), Xinhua said Pollution levels 30 times the World Health Organization's recommended standard Government officials blame lack of wind as well as farmers burning crop stalks (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. 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. Hazardous levels 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. Could smog choke China's sporting ambitions? 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 heating 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. Extreme conditions Fang Lijuan, the city's chief meteorologist, said it was 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. Naming and shaming Last month China announced plans to start listing its top ten most air-polluted cities every month in the hopes that national humiliation will push positive environmental action. "We must put air quality control as an ecological red line for economic management and social development," China's Vice Premier Zhang Gao Li said in a statement as he announced the new policy at the 18th Air Pollution Control Conference in Beijing. Chinese officials did not say when the first list would be announced, but the northern megacities of Beijing and Tianjin, as well as the surrounding provinces of Hebei, Shanxi, Inner Mongolia and Shandong have signed onto an official plan to speed up air pollution control measures. China's capital often suffers with hazardous pollution levels and smog. An explosion in the number of cars on the roads, as well as industrial pollution are seen as the main contributors. CNN's Feng Ke in Beijing contributed to this report.