NEW DELHI (AFP) - Some 1,800 primary schools in New Delhi were ordered to shut down on Saturday (Nov 5) as the Indian capital grapples with some of the worst pollution in recent years, an official said.

The decision would affect 900,000 children studying at schools run by the Municipal Corporation in a city which has been enveloped by a thick smog since last weekend's Deepavali festival celebrations.

"It has been decided to keep the municipal schools shut on Saturday because of smog in Delhi," Mr Yogendra Mann, spokesman for the Municipal Corporation of Delhi, said.

"The schools will operate as normal from Monday (Nov 7)."

Most schools in India operate for six days a week, although Saturdays are a half-day.

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 (Oct 30) night for Deepavali when millions of firecrackers were set off, leaving the city blanketed in smog overnight.

The reading for pollutants in the atmosphere breached the 1,000 microgram-mark for the first time in one neighbourhood in south Delhi - 10 times the World Health Organisation's recommended level.

A new study by Unicef says some 300 million children live with outdoor air so polluted it can cause serious physical damage, with the situation most acute in South Asia.

On Friday (Nov 4), India's environment ministry called a meeting with officials of neighbouring states to discuss ways to combat pollution.

In Delhi's satellite city of Gurgaon, some schools remained closed on Friday, while others cancelled physical education classes and outdoor activities.