The air quality is expected to improve later in the day.
The air quality in Delhi today deteriorated beyond the "severe" level because of a ground-level dust storm in western India that had increased coarser particles in the air, the Central Pollution Control Board (CPCB) data showed.
The CPCB data showed that the PM10 (particles with diameter less than 10mm) level was beyond "severe" at 778 in Delhi-NCR area and 824 in Delhi particularly, leading to hazy conditions and limiting visibility.
Gufran Beig, a scientist at the centre-run System of Air Quality and Weather Forecasting and Research institute, said the dust storm deteriorated the air quality in Delhi-NCR.
"There was a ground-level dust storm in the western part of the country that increased drastically coarser particles in the air, causing a spike in pollution levels in Delhi," he said.
But the air quality should improve later today, he said.
"Such dust storms accompanied by high-speed winds (30-40 kmph) do not last too long due to which the air quality will return to normal by this evening," Mr Beig added.
According to CPCB, the air quality index at several places in Delhi crossed the 500-mark, with east Delhi's Anand Vihar area recording an AQI of 891.
An AQI between 0-50 is considered "Good", 51-100 "Satisfactory", 101-200 "Moderate", 201-300 "Poor", 301-400 "Very Poor", and 401-500 "Severe".