The air quality in the Indian national capital plummeted to the "severe" category after remaining in the "very poor" level for the past seven days.
On Tuesday, the air quality index in New Delhi crossed 400, prompting the government to issue health warnings for the 12th time in two months.
Officials have been warned against stepping out of their homes and exposing themselves to the toxic environment.
In November, schools in the city were forced to shut down for four days after the index climbed past 500.
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