Smog has continued to engulf major cities of Punjab as the ranking of Air Quality Index (AQI) has reached 413 today (Friday).

Residents choking in acrid smog pleaded with officials to take action. Air pollution has worsened in Pakistan in recent years, as a mixture of low-grade diesel fumes, smoke from seasonal crop burn off, and colder winter temperatures coalesce into stagnant clouds of smog.

Lahore, a bustling megacity of more than 11 million people in Punjab province near the border with India, consistently ranks among the worst cities in the world for air pollution.

In recent years residents have built their own air purifiers and taken out lawsuits against government officials in desperate bids to clean the air -- but authorities have been slow to act, blaming the smog on India or claiming the figures are exaggerated.