Delhi chokes as pollution levels hit the worst

Pollution levels in New Delhi have hit their worst this year in the past two days - earning a "severe" to "emergency" rating and indicating conditions that can spark a public health crisis.

Christmas Day in the Indian capital is also forecast to be bleak.

Senior government officials said the main reasons for the surge in the amount of toxic smog trapped over New Delhi were unusually cold air, including fog, and a lack of wind.

This mean that vehicle fumes, pollution from coal-fired power plants and industries, as well as smoke from fires being burned to keep people warm hangs over the city.

Data from the government's Central Pollution Control Board (CPCB) showed the air quality index, which measures the concentration of poisonous particulate matter, was an average of 449 yesterday, only slightly better than the 450 on Sunday.

Anything above 100 is considered unhealthy.