Air pollution levels in the Indian capital of New Delhi today have peaked at a level 20 times the World Health Organisation's set safe limit. 

The city has been choked on and off for weeks, as industrial and traffic pollution - combined with smoke from crop stubble burning - cast a toxic pall over the Asian metropolis.

On Wednesday, for the second time in 10 days, the amount of 2.5PM - the deadly tiny particles that could into the bloodstream and lungs - hit 'emergency' levels, well above the safe limit set by the WHO. 

The overall air quality index (AQI) in Delhi was 494, according to the monitoring agency SAFAR.

The index measures the levels of the airborne particles that can reach deep into the lungs.