Supreme Court asked authorities on Thursday to report back within a week on what they were doing to stop farmers from burning crop residue as smog began to pollute the air in the capital Delhi and surrounding regions, local media reported.

Farmers in the northern states of Punjab, Haryana and Uttar Pradesh burn crop stubble after rice is harvested around October to clear the fields before planting wheat crops.

The smoke contributes to a toxic smog that engulfs Delhi, frequently making it the world's most polluted capital ahead of winter as calm winds and lower temperatures trap pollutants in the air.

Federal and state authorities have encouraged farmers to stop burning crop residue and penalised those that do but have not been able to fully curb the practice due to the large area involved and the hostility of farmers in some places.

"In some of the districts in Punjab and Haryana the incidents of stubble burning increased substantially as compared to 2023," legal news website Live Law reported the court as saying. "However, all (that) the states have done is to recover nominal compensation from 42 and 45 farmers respectively."

A government website monitoring crop burning showed about 200 fires almost every day in Punjab, Haryana and Uttar Pradesh since the middle of September.

The court also pulled up the Commission for Air Quality Management, a government body responsible for air quality in the national capital region, saying it "does not seem to be making any efforts to follow up implementation of its own directions".

The court asked the commission, which did not immediately respond to a request for comment, and state authorities to report within one week on the action being taken to stop crop residue burning.

India was rated the third most polluted country last year by Swiss group IQAir, behind Bangladesh and Pakistan. New Delhi ranked sixth on a real-time list of the world's most polluted cities with the air quality index at 115 on Thursday, a level considered unhealthy for sensitive groups.

India's weather office has forecast moderate air quality in the capital until Oct. 6 and then moderate-to-poor for six days after that.

Experts fear air quality could further deteriorate from mid-October when farm fires are expected to increase before peaking towards the end of the month and beginning of November.