Toxic smog in India and Pakistan has caused air quality in the major metropolitans of Lahore, Multan, Delhi and Chandigarh to deteriorate to toxic levels.

The government in Lahore has closed schools and public spaces and shut down factories. Environmental lawyer Ahmad Rafay Alam shares his perspective: "frustrated" but still fighting.

Pakistan’s cities slip under toxic smog as live readings for Lahore show PM2.5 levels 100 times over what WHO prescribes

Record-breaking levels of thick, toxic smog that have shrouded eastern Pakistan and northern India since last month can be seen in striking satellite imagery.

Lahore and its 13 million residents have now been choking for a week; the air quality index has passed the 1,000 mark repeatedly this month - anything above 300 is considered hazardous. Pakistani officials have scrambled to respond to the crisis - its scale unprecedented even in a city which deals with smog at this time each year.

With cities in India and Pakistan ranking among the world's most polluted, new technologies must be adopted to tackle dangerous levels of winter smog, environmentalists urge.

The satellite images show an extremely heavy grey smog over Pakistan. It stretches into northern parts of India, albeit is lighter than the one over its neighbouring country.