"Keeping in mind the hazardous exposure to children ... all schools must remain shut for the next two days," Bhure Lal, the chairman of the Environmental Pollution Prevention and Control Agency, said in a letter to the city government of Delhi and to its neighboring states.
The Central Pollution Control Board said that the air quality index was 472, nine times the level recommended by the World Health Organization. The maximum possible rating is 500.
Air pollution in northern India peaks in the winter due to smoke from agricultural fires. The smoke from fields mixes with vehicle emissions and construction dust, making it the world's most polluted capital.
The smog was not enough to put off the more than 1,000 children participating in a race on Thursday morning. The annual "Run for Children" event is organized by a not for profit group called Prayas. Asian news network ANI reported on the run.
"The children did not run a long distance. It was a short run," said Prayas' general secretary, Amod K. Kanth.
Kanth has received criticism for allowing the run to go ahead in such conditions.