Air quality in Delhi hit severe levels on Friday and a thick toxic smog cloaked the city, marking the beginning of a pollution season that has become an annual catastrophe for India’s capital.

Schools were shut and non-essential construction was banned around Delhi as the air quality index in the city almost hit 500 – the highest the measurement will go and 100 times the limit deemed to be healthy by the World Health Organization.

Air quality in the city had deteriorated over the past week, attributed to a sharp rise in farmers in the neighbouring states of Haryana and Punjab burning their fields during the crop planting season, compounded by winds that carried the pollutants into Delhi and a drop in temperatures trapping the particles.

On Sunday, the state of Punjab saw a 740% increase in farm fires, with more than a thousand recorded in a single day.

It is time for us to wear masks and go out only when needed,” said Nikhil Modi, a doctor at Apollo hospital in Delhi.

Methods deployed by the AAP government to tackle pollution have included the sprinkling of water on roads to reduce dust and the building of two 80ft high “smog towers”, costing more than $2m each, that are supposed to clean the air but have been deemed by scientists to be largely ineffective.

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