The manager for US jazz singer Patti Austen, 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 start on a specific date.
"I couldn't see anything outside the window of my apartment, and I thought it was snowing," said 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 ahead of him and that his usual bus had stopped running.
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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 the monitoring could give readings higher than that.
A safe level recommended by WHO is 25 micrograms per cubic meter.
Some of the city's buses also stopped running, the official Xinhua News Agency said.
Austin's management team said the 63-year-old singer had been treated in hospital Friday morning for the asthma attack in combination with respiratory infection. She returned to her hotel later Friday to rest, but she was unable to physically perform at her concert scheduled for Beijing on Friday evening. Her Saturday night concert in Shanghai went ahead.