The decision follows a comprehensive review of air quality and weather forecasts from the India Meteorological Department (IMD) and IITM, which indicate a likelihood of the AQI remaining in the "very poor" range in the coming days.

GRAP stage 3 will come into force at 8am on Friday. The Delhi government announced that classes for primary schools will be shifted to online.

In a repeat of what occurs every year, Delhi is engulfed by toxic smog as air quality remained in the "severe" category at the onset of winter in the national capital, media reports said.