The air quality index of the US Embassy in New Delhi stood at “hazardous” levels of 497 as of 0630 GMT, with levels of airborne PM 2.5 - particles that can reach deep into the lungs - touching nearly 700 in parts of the city.
That is more than 10 times the recommended safe limit of 60 for PM 2.5.
A dip in wind speed and temperature is making air denser, trapping pollutants and worsening air quality, said Vivek Chattopadhyay, a senior programme manager at New Delhi-based non-profit Centre for Science and Environment.
The city government of Delhi, a metropolis of over 20 million, is restricting the use of private cars until November 15 with an “odd-even” system - allowing cars on alternate days, depending on whether their licence plate ends in an odd or even number.
The scheme, which includes a two-day waiver for a religious festival, has helped little, prompting environmentalists to call for urgent action.
“The chief minister (of Delhi) needs to declare an emergency,” said Bharati Chaturvedi, founder of the Chintan environmental advocacy group.