Air pollution several times worse than safe limits has crippled Delhi for the last week. (AFP)

Highlights Thick smog in Delhi has worsened since Diwali

Pollutants as high as 13 times the safe limit in Delhi today

Can cause respiratory diseases if subjected to prolonged exposure

Pollution in Delhi has worsened since Diwali this last week. (AFP photo)

Vehicles and coal-fired power plants add to Delhi's pollution. (AFP photo)

Some 1,800 primary schools in New Delhi have been ordered to shut down today as the national capital grapples with some of the worst pollution in recent years.The decision affects around 9 lakh children studying at schools run by the municipality in a city which has been enveloped by thick smog since last weekend's Diwali festival celebrations Data from the city's pollution monitoring agency showed that concentrations of Particulate Matter or PM 10 (coarser pollutants) was over 1,200 micrograms per cubic metre this morning compared to a safe level of 100 at around 9 am in Delhi's Anand Vihar. PM 2.5, a standard measure of air quality, was as much as 13 times the safe limit.These particles can cause respiratory diseases if one is subjected to prolonged exposure to unsafe levels."It has been decided to keep the municipal schools shut on Saturday because of smog in Delhi. The schools will operate as normal from Monday," Yogendra Mann, spokesman for the Municipal Corporation of Delhi, told AFP.New Delhi's air quality has steadily worsened over the years, a consequence of rapid urbanisation that brings pollution from diesel engines, coal-fired power plants and industrial emissions.It also suffers from atmospheric dust, the burning of crop stubble in farms around the city and pollution from open fires lit by the urban poor to keep warm in winter or to cook food.The latest crisis began in the aftermath of the celebrations last Sunday night for Diwali when millions of firecrackers were set off, leaving the city blanketed in smog overnight.

On Friday, the environment ministry called a meeting with officials of neighbouring states to discuss ways to combat pollution.A report released by UNICEF on Monday had said around 6 lakh children under age 5 die every year - more than malaria and HIV/AIDS combined - from diseases caused by or exacerbated by outdoor and indoor air pollution.