NEW DELHI -- Several areas in the Indian capital faced "Severe" air pollution levels on Sunday, even as the Air Quality Index (AQI) crossed the 400-mark and a dense smog enveloped the city.

Experts said that people living in Delhi should regularly use air purifiers. There was said to be a surge in the number of people suffering from respiratory problems, said doctors.

Several areas, including Anand Vihar, Chandni Chowk, Nehru Nagar, R.K. Puram, Rohini, recorded an AQI of over 400 thus making the air quality in these areas as "Severe".

An online report by The Indian Express quoted pulmonologist Gopi Chand Khilnani as saying that those suffering from respiratory diseases should leave Delhi for the next few weeks so as to keep themselves away from the city's air pollution.

Over the past few days, the Delhi government has been using air-guns in an attempt to reduce air-pollutants in the atmosphere. Strict anti-air pollution measures, like a ban on open burning of coal and usage of diesel generators, were already in place.