Pollution levels have spiked in Pakistan's second-largest city of Lahore as a dense smog blankets the area. The situation has prompted the government to make face-masks mandatory to protect people's health.

A Swiss-based air quality watchdog reports that Lahore in Punjub province became the world's most polluted city on Monday. Amid the worsening situation, the provincial government on Tuesday began enforcing mandatory mask-wearing.

A man who bought a mask said: "Smog is making our children and adults sick. We're wearing masks to shield ourselves from sore throats, coughing, and other health issues."

Local officials also announced that children and students with respiratory and cardio-vascular conditions should stay at home and take online classes.

Air pollution in Lahore has become a serious problem as the economy grows. The situation deteriorates as winter approaches partly due to crop burning for the wheat-planting season.