New Delhi, Dec. 21 -- Air pollution surged into the severe category in Delhi on Saturday while blinding fog and frigid temperatures swept much of northern India and disrupted air, road and rail traffic across 10 states as authorities issued red and orange alerts for swathes of the Indo-Gangetic plains.

The maximum temperature plunged to 16.9 degrees Celsius - 5.3 degrees below normal and the season's coldest morning yet - meeting the criteria for a cold day. Delhi's air quality index (AQI) climbed to 410 at 11pm, breaching the severe threshold.

A satellite image captured at 9am revealed the scale of the crisis: a continuous band of fog stretching from the Kashmir valley through Punjab, Haryana, Delhi, Uttarakhand, Uttar Pradesh, Bihar, ...