Firecracker ban defiance makes New Delhi the world's most polluted city

New Delhi topped charts on Friday as the world's most polluted city after revellers defying a ban on firecrackers to celebrate Diwali, the Hindu festival of lights, helped drive air quality to hazardous levels.

Thick smog wreathed the Indian capital, shrouding the presidential palace in the central district and the surrounding gardens popular with joggers and cyclists, after Thursday's celebrations.

The air quality index stood at 348, said Swiss firm IQ Air, taking pollution into the hazardous category, pushing Delhi to the top of a real-time list as the world's most polluted city.

Local government officials have banned use of firecrackers during Diwali and the winter over the last few years, in line with Supreme Court directives, but have had difficulty enforcing the measure despite the threat of jail.

Some groups say the ban interferes with observance of the festival, a position the Delhi government has previously countered by saying the ban aims to save lives.

Friday's smog also coincided with waste burning on farms in northern India that aggravates air quality at the beginning of winter each year as cold, heavy air traps pollutants from a variety of sources.