Choking smog all but shut down one of northeastern China's largest cities Monday, forcing schools to suspend classes, snarling traffic and closing the airport in the country's first major air-pollution crisis of this fall and winter.
Smog — a mixture of atmospheric pollutants, including car exhaust and factory emissions — is measured on an air-quality index measuring PM2.5, or particulate matter less than 2.5 micrometers in diameter. A level above 300 is considered hazardous, and the World Health Organization recommends a daily level of no more than 20.
In some parts of Harbin, the gritty capital of northeastern Heilongjiang province and home to some 11 million people, readings reached 1,000.
The smog not only forced all primary and middle schools to suspend classes but also shut the airport and some public bus routes, the official Xinhua news agency reported, blaming the emergency on the first day of the season that heating was turned on in the city. Visibility was reportedly reduced to 10 meters.
The smog is expected to continue for the next 24 hours.
Related: Outdoor air pollution a leading cause of cancer
The World Health Organization has classified outdoor air pollution as a leading cause of cancer in humans. The declaration that air pollution is a carcinogen, alongside dangers such as asbestos, tobacco and ultraviolet radiation, came after a consultation by an expert panel.
Air quality in Chinese cities is of increasing concern to China's stability-obsessed leadership because it plays into popular resentment over political privilege and rising inequality in the world's second-largest economy.
Domestic media have run stories describing the expensive air purifiers that government officials enjoy in their homes and offices, alongside reports of special organic farms so the elite need not risk suffering from tainted food amid recurring food-safety scandals.
The government has announced plans over the years to tackle the pollution problem but has made little apparent progress.
Users of China's popular Twitter-like Sina Weibo microblogging site reacted with anger and bitter sarcasm over Harbin's air pollution.
"After years of effort, the wise and hardworking people of Harbin have finally managed to skip both the middle-class society and the communist society stages, and have now entered a fairyland society!" wrote one user.
While censors typically delete politically subversive comments on social-media sites like Sina Weibo, it appears authorities have, for some reason, allowed messages on environmental issues to remain.
Other parts of northeastern China also experienced severe smog, including Tangshan, two hours east of Beijing, and Changchun, the capital of Jilin province, which borders Heilongjiang.
Last week Beijing city released a color-coded alert system for handling air-pollution emergencies, with responses including temporary halts to construction, factory production, outdoor barbecues and the setting off of fireworks.
Beijing suffered its own smog emergency last winter when the PM2.5 surpassed 900 on one particularly bad day in January.
Al Jazeera and Reuters