Northern India encountered the recurring annual pre-winter event of air emergency where the Air Quality Index (AQI) readings of main pollutant PM 2.5 breached the 400-mark of “very poor” and landed the air of Delhi, Punjab and other northern cities into the “hazardous” category.

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.