Fireworks set off during celebrations for Diwali, the Hindu festival of lights, could further worsen air quality in the Indian capital this week, officials said on Tuesday, offsetting a reduction in burning of farm waste in nearby states.

Rated the world's most polluted capital by Swiss group IQAir for four years in a row, New Delhi was the world's second most polluted city on Tuesday, the group's live rankings showed, after Lahore in neighbouring Pakistan.

"The incidents of stubble burning are decreasing, but ... the smoke created by firecrackers needs to be controlled," Delhi Environment Minister Gopal Rai told news agency ANI, calling for further monitoring of the burning of farm waste.

The annual practice of burning crop stubble left after harvesting paddy to clear fields for wheat planting is widely blamed for toxic pollution in the region before winter, causing disruptions such as school closures and construction curbs.

But people often flout Delhi's ban on smoke-emitting firecrackers, usually burnt in celebration of the festival which runs from Wednesday to Friday this year, worsening pollution.

Delhi's air quality was 273 on Tuesday, the Central Pollution Control Board's index showed, far exceeding a rating below 50 that is considered to be 'good'.

From Wednesday to Friday, the index is expected to be in 'very poor' territory from 301 to 400, but may drop to 'severe' in the index range of 401 to 500, fed by fumes from burning firecrackers and waste fires, the earth sciences ministry said.

Air quality is likely to be in the very poor to severe category for six days from Saturday, the ministry added.

Farm fire incidents have fallen this year, however, the agriculture ministry said, to stand down 35% in Punjab and 21% in Haryana - both breadbasket states - compared to the corresponding period in 2023.

Data from the earth sciences ministry showed that stubble burning's contribution to pollution dropped in the last week, to reach barely 3% on Monday from 16% on Wednesday, with greater contributions from other sources, such as vehicles.

Last week, the Supreme Court urged authorities in Delhi and adjoining states to tackle the toxic air, saying living in a pollution-free environment was a "fundamental right".