Beijing - Beijing issued its second-ever red alert for smog on Friday ahead of severe pollution forecast to hit China's capital, weeks after putting its emergency response plan into action for the first time.
The notice from the capital's environmental bureau orders factories to close and pulls half of all private cars off the streets, among other measures, as bad air floods into the city for the third time this month.
The red alert, the highest tier of a four-colour warning system, will last from Saturday to Tuesday, according to the notice on the Beijing Municipal Environmental Protection Bureau's website.
It will be the second time the highest level alert has been issued since the city established a pollution warning system in 2013.
Beijing issued its first red alert on 7 December, declaring emergency pollution measures following scathing public criticism of the city's weak response to December's first round of smog, when pollution skyrocketed to some of the worst levels this year.
Counts of PM2.5 - harmful microscopic particles that penetrate deep into the lungs - regularly exceeded 300 micrograms per cubic metre during last week's red alert, according to the US embassy, which issues independent readings.
The World Health Organization's recommended maximum exposure is 25 over a 24-hour period.
Beijing lifted the alert on 10 December, after winds from the north dispersed the bad air, leaving skies clear and blue.
Other cities in the region will also raise their alert level to red, the national environmental bureau said in a separate statement, adding it had urged regional governments to "implement heavy air pollution emergency response measures".