BEIJING (AP) ― Beijing schools canceled outdoor flag-raisings and took sports classes indoors while hospitals saw a spike in respiratory cases Monday because of the extremely hazardous air in China’s notoriously smoggy capital following a weekend of off-the charts pollution.

City authorities ordered many factories to scale back emissions, and were spraying water at building sites to try to tamp down the dust and dirt that worsens the noxious haze that has hung over the city since late last week.

Demand spiked for face masks and air purifiers, and hospitals saw surges of up to 30 percent in residents seeking help for breathing problems, state-run media outlets reported. Schools in several districts were ordered to cancel outdoor activities, and in an unusual public announcement, Beijing authorities advised all residents to “take measures to protect their health.”

“It’s really terrible. I’m extremely upset, but there’s really nothing much I can do,” said a Beijing resident out for a morning stroll. Like many Chinese, the man would give only his surname, Kang.

Another man, a 60-year-old retiree surnamed Chen, said his elderly relatives had moved to stay with family members outside the city to avoid the pollution. “I’m in pretty good shape, but the older folks have a lot of problems with their hearts -- breathing, and high blood pressure,” Chen said.

Levels of PM 2.5 particle pollution over the weekend reached the highest levels since the Beijing government began publicly releasing figures early last year, and in separate monitoring by the U.S. Embassy, they were at 886 micrograms per cubic meter in a reading that was labeled “beyond index.”

By Monday levels had declined to 245 micrograms on the Beijing government scale -- down from a high above 700 -- but still way above the level of 25 considered safe by the World Health Organization.

PM 2.5 are tiny particulate matter less than 2.5 micrometers in size, or about 1/30th the average width of a human hair. They can penetrate deep into the lungs, and measuring them is considered a more accurate reflection of air quality than other methods.

Beijing’s air started to worsen on Thursday, and Beijing’s monitoring center said the pollution was expected to linger until Tuesday.