Delhi, meanwhile, witnessed one of its worst smog of the season, with visibility remaining less than 800 metres through Monday. PM 2.5 levels were in the 'severe' category in many parts of the city, with the most polluted spot, Anand Vihar, showing levels up to 530 mcg/cubic m between 2.30pm and 8pm.

Despite being labelled by the WHO as the world's most polluted city, there's no protocol in Delhi for warning residents when pollution levels spike. PM 2.5 levels at individual air monitoring stations have in the past few days crossed the 600 mark.

Many residents complained of a choking feeling as a white smog hung in the air through the last day of November, a month that saw Delhi's air quality dip alarmingly.

"Monday morning (6-8am) saw the densest fog of the season in Delhi. In November, such thick fog usually forms only after rain, when moisture levels go up. Since there has been no rain, it's likely high pollution, combined with moisture and absence of winds caused the fog," said R K Jenamani, director of Met office at IGI Airport.