Delhi blanketed in thick smog

New Delhi's overall Air Quality Index (AQI) stood at 456 on a scale of 500, indicating "severe" pollution conditions that can affect healthy people and seriously impact those with existing diseases.

"The situation in north India, not just in Delhi but in entire north India is becoming extremely severe," said environmentalist, Vimlendu Jha.

The AQI measures the concentration of poisonous particulate matter PM2.5, which can cause cardiovascular and respiratory diseases such as lung cancer, in a cubic metre of air.

On social media, some residents complained about the hazardous conditions in Delhi, which has the worst air quality of all world capitals, with an annual spike often early in the winter.

Toxic air kills more than a million people annually in India and takes an economic toll on the country's populous northern states and the capital city of 20 million people.