New Delhi: As Delhi woke up to a white cover of fog on Tuesday morning, pollution levels in the national capital was ‘severe’ for the second time since Diwali.

While an Air Quality Index (AQI) between 0-50 is considered good, Delhi’s average AQI was 411 at 9am on Tuesday morning, which is read as severe. According to the IMD, visibility also took a plunge and it was way below 200 metres.

According to ANI, at least 20 flights were affected at the Delhi airport

The Indian Medical Association (IMA) has also written to the Delhi government, advising it to stop outdoor activities and sports at schools in the morning. With the pollution levels in the city going up by 12-19 folds than the permissible limits, the medical body has issued a warning.

Meanwhile, Delhi Chief Minister Arvind Kejriwal has blamed the rising pollution levels to crop burning in adjoining states. In a tweet, he said: "We have to find a solution to crop burning in adjoining states."

Delhi has become a gas chamber. Every year this happens during this part of year. We have to find a soln to crop burning in adjoining states — Arvind Kejriwal (@ArvindKejriwal) November 7, 2017

A majority of the 18 pollution monitors installed by the Central Pollution Control Board (CPCB), Delhi Pollution Control Committee and the Indian Meteorological Department read 'severe'.

The worst reading was at Shadipur, West Delhi, where the AQI was 448, while Anand Vihar's AQI was at 422, up from 411 at 10 pm on Monday night. RK Puram, another heavily polluted spot in the city was at 414 and Punjabi Bagh at 420.

Mathura Road was also at 441, which is one of the highest in the city.

The IMA has also asked the upcoming Delhi Half Marathon to be cancelled. In two letters to Deputy Chief Minister Manish Sisodia, IMA National President Dr KK Aggarwal and the Honorary Secretary General Dr RN Tandon said that school children are "especially at risk", with air quality ranging from 'poor' to 'severe'. So are the runners who will face the high morning pollution levels when the marathon starts at 7 am on November 19.

With the morning air going to severe levels, it becomes all the more hazardous for school and college-going students and office goers.

Students at North Campus were faced with more risk at the AQI measured 425 here. Morning walkers at Lodhi Road were also faced with an equally polluted air with an AQI of 407 and 408 at Siri Fort area.

According to CPCB, a city hits 'severe' when it's AQI is between 401 and 500 and the two primary pollutants, PM10 and PM2.5, are above 430µg/m3 and 250µg/m3 respectively.

Delhi's air, right now, is dangerous even for healthy people, which inevitably has a serious impact on those who are already ailing.