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Schools in Delhi, the capital of India, are to close for a week because the smog has got really bad.

At the weekend, levels of pollution in the capital were 20 times the maximum daily limit recommended by the World Health Organization.

Health officials have asked people to stay indoors and not do any outdoor activity to avoid getting ill from it.

Twenty-two of the world's 30 most polluted cities are in India, according to a Swiss report in 2020 and Delhi ranked the most polluted capital globally.

A pollution lockdown began on Sunday 14th November.

The Government has said that no construction will be allowed for four days and government workers were asked to operate from home.

"Starting Monday, schools are being shut so that children don't have to breathe polluted air," Delhi's chief minister, Arvind Kejriwal said.

Earlier this year, the Delhi government opened its first "smog tower". It was a $2 million installation that can half the amount of harmful particles in the air in a small area.

The government has said that this pollution has been caused by "heavy sewage" and "industrial waste", although Delhi has had high levels of pollution for many years and it often rises around this time of year.

Experts think the main reason that the air pollution is so bad at the moment is because of farmers burning crops.

It's done to clear their fields ready for the next crops, and burning is a cheap and easy way of doing it but it can cause big problems for air pollution.

The Supreme Court of India banned farmers from burning their crops, but lots of farm fires have still happened this year.