BEIJING — Visibility shrank to less than half a football field and small-particle pollution soared to a record 40 times higher than an international safety standard in one northern Chinese city as the region entered its high-smog season.

The manager for U.S. jazz singer Patti Austin, meanwhile, said the singer had canceled a concert in Beijing because of an asthma attack likely linked to pollution.

Winter typically brings the worst air pollution to northern China because of a combination of weather conditions and an increase in the burning of coal for homes and municipal heating systems, which usually starts on a specific date. For the large northern city of Harbin, the city’s heating systems kicked in on Sunday, and on Monday visibility there was less than 50 meters (yards), according to state media.

“I couldn’t see anything outside the window of my apartment, and I thought it was snowing,” Wu Kai, 33, a housewife and mother of a baby boy, said in a telephone interview from Harbin. “Then I realized it wasn’t snow. I have not seen the sun for a long time.”

She said her husband went to work in a mask, that he could barely see a few meters (yards) ahead of him and that his usual bus had stopped running.

“It’s scary, too dangerous. How could people drive or walk on such a day?”

The density of fine particulate matter, PM2.5, used as an indicator of air quality was well above 600 micrograms per cubic meter — including several readings of exactly 1,000 — for several monitoring stations in Harbin, according to figures posted on the website of China’s environmental protection agency. They were the first known readings of 1,000 since China began releasing figures on PM2.5 in January 2012, and it was not immediately clear if the devices used for monitoring could give readings higher than that.

A safe level under WHO guidelines is 25 micrograms per cubic meter.

Primary and middle schools and some highways were closed, said authorities in the city, which is in China’s northernmost province bordering Russia. At least 40 flights to destinations in southern China and Beijing among others were canceled or postponed at Harbin’s Taiping International Airport on Monday morning.