Schools affected by smog in parts of South Asia

Image source, EPA

School children in some areas of Pakistan have been told they won't be taking part in outdoor activities until the end of January 2025 because of an increase in air pollution.

Lahore became the world's most polluted city on Monday when the Air Quality Index (AQI) hit hazardous levels.

The AQI measures pollution levels in the air.

Health officials in Pakistan have asked the most vulnerable people to stay inside.

The Environment Protection Department Punjab issued a high alert warning last week.

Image source, EPA

Image caption, Lahore in Pakistan is one of the world's most polluted cities

Meanwhile, air quality levels in India's northern states have also been affected.

In India's capital city Delhi, pollution levels were more than 30 times the World Health Organisation's safe limit in several areas.

Weather conditions, the burning of crops and the use of firecrackers during the Hindu festival of Diwali could add to the problem.

Image source, Getty Images

Image caption, School lessons for many children have been affected

Farmers burn the remaining stubble of their harvested crops during the months of November and December in order to clear the fields to make way for more planting.

But this can cause huge amounts of smoke, lowering the overall air quality in the surrounding regions.