Delhi air quality deteriorated on Monday as residents set off fireworks for Diwali, violating court orders. The city recorded a very poor air quality index of 370. Many areas showed severe levels of pollution, leaving residents struggling. Smog covered India Gate as the city faced this annual winter health problem.

Nov 9 (Reuters) - Air quality deteriorated in India's capital Delhi on Monday, after residents celebrating the Hindu festival of lights set off fireworks ​in violation of court orders.

At 9 a.m. (0330 GMT) on Monday, ‌Delhi recorded an air quality index of 370, categorised as 'very poor' by the Central Pollution Control Board, which considers an AQI of up to 50 ​to be 'good'.

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Many areas in the city of 20 million showed ​a reading of more than 400, categorised as 'severe', official ⁠data showed.

India's Supreme Court said earlier this month that only certified ​low-polluting firecrackers would be allowed to be used during limited hours ​over the Diwali weekend.

Residents in Delhi and in Mumbai, the country's financial capital, said firecrackers were going off until late in the night.

Visuals from Reuters TV ​showed a layer of smog enveloping India Gate, a prominent spot ​in central Delhi, close to government offices and parliament.

Delhi was the third-most polluted ‌city ⁠in the world as of Monday morning, Swiss group IQAir's live ranking showed, with Pakistan's Lahore at the top with an air quality index of 563, which is categorised as hazardous.

Pollution is an ​annual problem in many ​parts of ⁠northern India from the onset of winter as cold, heavy air traps vehicle emissions, construction dust and ​smoke from crop waste burning.

The problem is exacerbated ​in big ⁠cities such as Delhi due to a high number of vehicles and construction activity, leaving many residents battling respiratory problems.

Delhi has seen poor ⁠air ​quality levels for more than a week, ​and imposed restrictions on Friday under a graded action plan, asking schools to conduct ​online classes, among other measures.