Pakistan’s second-largest city, Lahore, will close primary schools for a week over record pollution to avoid exposing millions of children to smog several times above levels deemed dangerous, according to AFP.

The news agency said that the city of 14 million people has been enveloped by smog, a mix of fog and pollutants caused by low-grade diesel fumes, smoke from seasonal agricultural burning and winter cooling.

The air quality index, which measures a range of pollutants, exceeded 1,000 on Saturday — well above the level of 300 considered “dangerous” — according to data from IQAir.

The Punjab government also recorded peaks of over 1,000 on Sunday, which is considered “unprecedented.”

“Weather forecast for the next six days shows that wind patterns will remain the same. Therefore we are closing all government and private primary schools in Lahore for a week,” Jahangir Anwar, a senior environmental protection official in Lahore told AFP.

“All the classes” for children up to the age of 10, “public, private & special education… shall remain closed for one week” from Monday until Saturday, read a local government decision seen by AFP.

The decision added that the situation will be assessed again next Saturday to determine whether to extend the school closure.

“This smog is very harmful for children. Masks should be mandatory in schools. We are keeping an eye on the health of children in senior classes,” Punjab senior minister Marriyum Aurangzeb told a news conference on Sunday.

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