One doctor compared breathing in Pakistan's toxic air to smoking "dozens of cigarettes a day" as Lahore is the world's most polluted city this week.

Punjab province in Pakistan has declared a health emergency and closed two cities due to severe smog affecting nearly 2 million people.

LAHORE, Pakistan — A Pakistani province declared a health emergency Friday due to smog and imposed a shutdown in two major cities. Smog has choked Punjab for weeks, sickening nearly 2 million people and shrouding vast swathes of the province in a toxic haze.