NEW DELHI, Oct. 25 (Xinhua) -- Air quality continued to worsen in the Indian capital for the fourth day in a row on Thursday ahead of Diwali, festival of lights, when pollution levels peak.

On Thursday morning, air quality index (AQI) dipped to 337, considered very poor category.

An AQI between O and 50 is said to be good, 51 and 100 satisfactory, 101 and 200 moderate, 201 and 300 poor, 301 and 400 very poor and 401 and 500 severe.

State-owned System of Air Quality and Weather Forecasting And Research (SAFAR) which records pollution levels has predicted very poor air quality in the next two days.

Delhi's air quality has been in the poor category since Monday.

Delhi's Environment Minister Imran Hussain Tuesday reviewed an action plan for implementing the Graded Response Action Plan (GRAP).

GRAP kicks in when AQI touches severe levels as mandated by the country's Supreme Court.

The Supreme Court has already ordered a partial ban on bursting of crackers during Diwali to keep pollution levels lower than in previous years.

The court ruled Tuesday that people in the country can burst firecrackers only from 8:00 p.m. to 10:00 p.m. local time on Diwali and only "green firecrackers" were allowed.