Toxic smog in eastern Pakistan has made thousands of people sick, forcing authorities to shut some cities for the rest of the week, Ednews reports citing BBC.

Smog in the country's second-largest city Lahore has risen to dangerous levels.

The Punjab provincial government has ordered that schools, offices, malls and parks in three cities, including Lahore, be closed until Sunday.

Pakistan's Punjab province borders the Indian state of the same name.

Over the past few days, Lahore's Air Quality Index - which measures the level of fine particulate matter in the air - have hovered around the 400 mark. AQI levels at or below 100 are generally thought of as satisfactory. Lahore borders the Indian city of Amritsar.

North India is also suffering from the impact of toxic smog.

Air pollution in the Indian capital Delhi has risen to alarming levels. On Tuesday, the air quality index for the Indian capital hit 300 on 7 November, nearly reaching the hazardous levels of 301-500.

Persistent exposure to smog can lead to longer-term health damage, including causing lung cancer.

Some experts believe the burning of crop residue to prepare for the winter planting season is a key cause of the air pollution.

Pakistan said last week that it will raise the issue with Indian authorities at a diplomatic level, local media reported, without giving further details.

But experts have noted that just as in India, farmers in Pakistan also resort to stubble burning to prepare for a new planting season.