SHANGHAI (Reuters) – A total of 79 Chinese cities have triggered air pollution alerts as severe winter smog covers wide swaths of the country, the official Xinhua news agency reported on Saturday.

As of Nov. 30, five cities had issued red pollution warnings, the most severe in China’s pollution warning system, 73 had issued orange warnings, the second-most severe, and one city had issued a yellow warning, triggering the implementation of emergency management and control measures, Xinhua reported.

The affected cities lie in and around the Beijing-Tianjin-Hebei region that includes China’s capital, as well as in the Fenwei plains area of Shanxi, Shaanxi and Henan provinces, and in the northern Yangtze River delta region, home to Jiangsu province, China’s second-largest steelmaking hub.

China’s capital issued its first air pollution alert for the winter season on Nov. 23, and Jiangu province issued orange smog alerts in late November, forcing factories and utilities to slash output.

Northern China often sees heavy smog over the winter, which runs from mid-November to mid-March, as homes and power utilities burn more coal for power and heating.

On Saturday evening, the concentration of small particulate matter, known as PM2.5, at Beijing’s Temple of Heaven was 193 micrograms per cubic meter, according to data from China’s National Environmental Monitoring Centre, five-and-a-half times the state standard of 35 micrograms per cubic meter.

China has taken steps to broaden its campaign against air pollution, including extending a monthly air quality ranking to 169 cities from 74 to pressure local authorities to clean up dirty skies.