Residents of China's northeastern city of Shenyang were urged to wear masks and follow safety protocols Sunday as air pollution rose to hazardous levels, and began covering part of Liaoning province.

Air Quality Index real-time data noted a concentration of PM 2.5 particles that extended to more than 1,000 micrograms per cubic meter, according to official data released by Shenyang Environmental Protection Agency.

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PM 2.5, or Particle Matter 2.5, refers to microscopic, toxic particles suspended in the air that are small enough to penetrate the lungs and enter the bloodstream.

A PM 2.5 concentration often results from the heavy combustion of materials, combined with organic compounds and metals. Its size is smaller than the human hair, and is linked to various respiratory illnesses, heart disease and cancer.

The pollution level apparently rose with the onset of winter, when people began burning coal to keep themselves warm.

Shenyang City's visibility level dropped to 100 meters, according to Chinese News Channel CCTV.

State news agency Xinhua posted various photos showing the city blanketed by smog. The photos carried the caption, "Fairyland or Doomsday?"

"The air stings and makes my eyes and throat feels sore when I'm outdoors," said a female resident who had to risk a quick trip outdoors to buy a mask.

The northern China residents burn coal to heat up their homes. This practice has been deemed one of the reasons for China's worsening air pollution.

Shenyang, an industrial city since the time of Mao Zedong, partially contributes to the industrial emissions and vehicle exhaust fumes that pollute Beijing and other cities.

TagsShenyang, China Air Pollution