Toxic smog choked Delhi as air pollution reached severe levels.

Locals experienced thick smog across the city, India's most polluted metropolis, reducing visibility to below 164 ft (50 m) on December 18.

Footage captured by Sumit Dookia shows visible smoke billowing in the air along a busy road.

Official data from the Central Pollution Control Board (CPCB) reported an alarming overall air quality index (AQI) of 433 in the 'severe' category as of 9 am on December 20.

Recent statistics from IQAir show that four cities in India ranked among the world's most polluted. Begusarai claimed the top spot, while Delhi was ranked third.

Delhi faces severe air pollution, with its nine million vehicles being a major contributor, particularly older diesel models. In the fall, crop burning by farmers in neighbouring states accounts for up to 45 per cent of the city's pollution, adding to the already critical levels caused by vehicle emissions.

Dust from construction sites and illegal industrial activities further exacerbates the problem, while coal-fired power plants, which generate over half of India's electricity, contribute significantly to the pollution burden.

Seasonal and geographical factors worsen Delhi's air quality. During winter, cold and stagnant air traps pollutants near the ground, while the landlocked geography of the Indo-Gangetic Plain limits their dispersal. Low wind speeds further prevent pollutants from clearing.

The use of firecrackers during Diwali also spikes pollution levels, making the city's air quality crisis more acute during the festival season.