NEW DELHI: A toxic smog shrouded the Indian capital on Tuesday, driving air quality in some areas into the “severe” range ahead of winter, when cold air traps pollutants and brings a spike in respiratory illnesses.

The mix of smoke, emissions, and dust is an annual problem for authorities in New Delhi, with vehicles, construction dust, and smoke from farm fires in the adjoining northern states of Punjab and Haryana among the major contributors.

“The outlook for the subsequent six days: the air quality is likely to be in the ‘very poor’ to ‘severe’ category,” said the earth sciences ministry.

The city’s overall score on an air quality index kept by India’s top pollution authorities was ‘very poor’ at 384, the ministry added, and was likely to stay there until Thursday.

An index range of 401 to 500 falls into the ‘severe’ category, implying it affects healthy people, but is more serious for those already fighting disease.

Ministry data showed farm fires have increasingly swelled the pollution over the last three days, for a share of more than 23 percent on Monday, from about 15 percent on Saturday.

About a third of the city’s 39 monitoring stations showed a ‘severe’ score of more than 400 on Tuesday, said the Central Pollution Control Board (CPCB), well short of an air quality score of zero to 50 that it rates as ‘good’.

Swiss group IQAir also rated Delhi the world’s second most polluted city on Tuesday, after Lahore in neighboring Pakistan, where authorities also took emergency measures in the wake of Sunday’s unprecedented pollution levels.

The government in the eastern province of Punjab, home to Lahore, has blamed deteriorating air quality on pollution wafting in from India, an issue it has vowed to take up with its neighbor through the foreign ministry.