Air pollution choking New Delhi has ground outdoor work to a halt and disrupted air travel in the Indian capital.

Every year, Delhi and northern states battle hazardous air during the winter months of October to January due to plummeting temperatures, smoke, dust, low wind speed, vehicular emissions and crop stubble burning. This time, experts say that the condition is likely to get worse in the coming days.

Air pollution in India's national capital increased to 'severe' on an official index on Wednesday for the first time this season as temperatures and wind speeds dropped, reducing visibility and affecting some flights.

A blanket of fog covered parts of Delhi for the second consecutive day on Thursday with the air quality index remaining in the 'severe' category, an official said