India, Dec. 15 -- Visibility plummeted to zero in parts of the national Capital as a thick layer of 'dense' to 'very dense' fog engulfed the region -- the first for this winter season -- combining with already high pollution levels in the region to create a toxic layer of thick smog which impacted flights and rail traffic in the early hours.

Over 400 flights were delayed at the Delhi airport until noon; at least 61 were cancelled and fiver diverted.

Delhi's air quality continued to remain at alarmingly high levels on Monday morning, with it firmly in the 'severe plus' category.

The 24-hour rolling average AQI stood at 452 at 9am -- marginally lower than a reading of 461 at 4pm on Sunday, which was December's second worst air day ever. ...