The air pollution in Delhi, India's most polluted city, continued to be above the "severe" level for the third day today as authorities cautioned people against staying outdoors for more than three to four hours.

The air quality worsened because of dust storms in western India, particularly in the desert state of Rajasthan, which increased coarser particles in the air, our Delhi correspondent reports quoting the Central Pollution Control Board (CPCB).

The PM10 level (presence of particles with diameter less than 10mm) was beyond severe at 796 in areas surrounding Delhi and 830 in Delhi particularly, leading to hazy conditions. A thick curtain of haze hung over Delhi and its adjacent areas since Tuesday.

The wind blowing in the region has contributed to the spread of dust particles. The dust-laden winds have created a haze in Delhi-NCR since Tuesday.

According to the CPCB, the air quality index - a measurement of the concentration of toxic particulate matter in the air - at several places in Delhi remained beyond the 500-mark, with east Delhi's Anand Vihar locality recording a PM10 level of 929 and PM2.5 level of 301 this morning, reports our Delhi correspondent.

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"

The Indian Environment Ministry has said the dusty conditions are likely to prevail for the next three days.

The CPCB said pollution this summer is very different from last year. In November, both PM2.5 and PM10 had spiked in the Delhi-NCR region, posing serious health hazard to residents.

However, the increase in pollution levels in summer is mainly due to drastic increase in coarse particles in the air, say experts.

A Sudhakar, CPCB member-secretary, warned people in Delhi and nearby areas that the pollution level is expected remain like this for 3-4 days and people are requested to avoid staying outdoors for more than three to four hours.

"There could be discomfort or breathing difficulties due to the pollution," Sudhakar cautioned.

"We have also called a meeting of construction companies and if the above severe condition persists, we would stop the construction activities," he said.