International: A thick toxic blanket of smog covering eastern Pakistan and entire northern India is seen in a striking satellite image released by American space agency NASA. It shows location pins for Lahore in Pakistan's Punjab and New Delhi, with both cities under huge cloud of grey smog. Lahore - a city of 14 million people stuffed with factories on the border with India - regularly ranks among the world's most polluted cities, but it has hit record levels this month.

Last week, live rankings by Swiss group IQAir gave the city a pollution index score of 1165. In New Delhi and neighbouring areas, it is hovering around 350. An Air Quality Index (AQI) of 50 or below is considered good with little risk of pollution.

The hazardous level of pollution has forced authorities in Pakistan to close schools till November 17 in a bid to lower children's exposure to the pollution.

In Multan, another city of several million people some 350 kilometres away, the AQI level passed 2,000 last week, according to news agency AFP. 

Access to parks, zoos, playgrounds, historic monuments, museums and recreational areas has also been banned along with tuk-tuks with polluting two-stroke engines and restaurants that operate barbecues without filters.

A "smog war room" has been set up in Pakistan's Punjab province where staff members from eight departments work towards controlling burning of farm waste and managing traffic.

A mix of low-grade fuel emissions from factories and vehicles and agricultural stubble burning blanket the city each winter, trapped by cooler temperatures and slow-moving winds.

According to World health Organisation (WHO), air pollution can trigger strokes, heart disease, lung cancer and other respiratory diseases.

It is particularly punishing for children and babies, and the elderly.

The chief pollutant is PM2.5, the fine particulate matter that poses greatest risk to health. It comes from sources like the combustion of fossil fuels, dust storms and wildfires, and has been linked to asthma, heart and lung disease, cancer, and other respiratory illnesses, as well as cognitive impairment in children.