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Beijing issued a blue alert for heavy air pollution Sunday morning.

The alert is forecast to last one day and people should take precautions and reduce outdoor activity, said a statement issued by the city's air pollution emergency response office.

At 10 a.m., readings at most of the city's monitoring stations for the hazardous fine particle matter PM2.5 exceeded 250 micrograms per cubic meter, according to Beijing Municipal Environmental Monitoring Center.

Air quality should improve Monday noon, the center said.

Beijing has a four-tier color alert system for pollution, with red being the highest, followed by orange, yellow and blue. The blue alert means the air quality index is forecast to reach between 200 and 300 PM2.5 for one day.