BEIJING (AP) — 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.

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Austin's management team said the 63-year-old singer had been treated in a hospital Friday morning for an asthma attack in combination with a respiratory infection. She returned to her hotel later Friday to rest, but was unable to perform at her Beijing concert scheduled for Friday evening. Her Saturday night concert in Shanghai went ahead.

Her manager, Barry Orms, said Monday that Austin, as an asthma sufferer, would have been "affected by the amount of pollution." He said that it wasn't their goal to place blame, and that "Patti has expressed our belief that the Chinese government can be a leader in this very important issue."

On the morning ahead of her concert Friday, Beijing's air was visibly polluted, with the city's environmental monitoring center warning children, the elderly and those with respiratory illnesses to reduce outdoor activity.

China's major cities have some of the world's worst smog. The government was long indifferent to the environment as it pursued economic development, but has begun launching some anti-pollution initiatives after mounting public frustration.

Last month, China's Cabinet released an action plan that aims to make a small reduction in the country's heavy reliance on coal to below 65 percent of total energy usage by 2017. According to Chinese government statistics, coal consumption accounted for 68.4 percent of total energy use in 2011.