China on Saturday issued a hazardous air alert after a heavy blanket of smog engulfed the capital city Beijing, urging residents to stay indoors.
Beijing air control authorities issued a "blue alert", the lowest of a four-level warning system on Saturday morning.
They blamed regional pollution and unfavorable weather conditions for the build-up of pollutants.
Beijing's air quality index (AQI) hit 276 at 12 pm, according to the Beijing Environmental Protection Monitoring Centre.
The office has ordered local pollution emitters to take further measures to cut emissions and advised residents to stay indoors and to wear masks when they venture out.
People suffering from respiratory and cardio-cerebrovascular diseases have been urged to reduce outdoor activities, state-run Xinhua News Agency reported.
The air is expected to gradually clear up over the next few days. Temperatures are likely to be as low as minus 7 degrees Celsius on Sunday in lowland and plain areas, according to the municipal meteorological station.