Pakistani second-largest city of Lahore will close primary schools for a week after seeing unprecedented pollution levels.

For days, the city of one point four 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 one thousand last Saturday well above the level of three hundred considered dangerous.