The Chinese capital city today issued an orange alert for air pollution in Beijing for the next three days starting midnight, cancelling outdoor activities in schools and construction projects in the smog-hit city.
The orange alert, the second highest in a four-tier warning system, will be effective from midnight today, according to the Beijing Municipality, the city's air pollution emergency response office.
An orange alert means heavy pollution - PM2.5 density of higher than 150 micrograms per cubic meter of air - for three consecutive days.
When the alert is in force, outdoor activities in schools are to be cancelled, and construction projects suspended.
The smog is expected to disperse Sunday evening when a cold front is forecast to hit the city, according to the city's meteorological authorities.
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Hundreds of flights have been cancelled in north China's port city of Tianjin because of the heavy smog that limited visibility on Sunday.
The municipal government has issued an orange alert for smog and haze on Saturday night.
An orange alert means heavy pollution -- PM2.5 higher than 150-- for three consecutive days.
A total of 309 flights have been cancelled, 15 forced to land in other airports and one returned, Xinhua reported.
Emergency plans have been activated to take care of the stranded passengers.
All highways in the city have also been closed, the city's transport authorities said Sunday afternoon.
Local weather bureau forecast the ongoing smog will continue till January 5 when a cold haze will disperse the pollution.
Tianjin is a frequent victim of smog that is common in the winter in north China, where cold weather and burning of dirty coal for heating combine to exacerbate the situation.