Toxic smog blanketed India's capital early Sunday after firecrackers were set off throughout the night to mark the country's biggest annual festival Diwali despite a ban, further worsening the city's air quality levels. 

India's environmental court had imposed a ban to stop millions of the explosives being lighted up to mark the Hindu Festival of Light, stressing that residents were already reeling from the impact of the coronavirus pandemic and the pollution crisis that arises every winter.

But the sound of firecrackers regularly was heard in the city of 20 million people late Saturday, and sporadically on Sunday.

"The overall air quality of Delhi is in the Severe category as of today morning," the state-run System of Air Quality Weather Forecasting and Research (SAFAR) said Sunday.

"Significant local additional emissions (probably firecracker related) during yesterday night... build up stubble fire-related pollutant concentrations."

But the meteorological body added that wind speeds in the capital were picking up on Sunday, helping to clear the choking air, while "isolated scattered rainfall" later in the day was also expected.

Delhi is infamous as having some of the world's dirtiest air, with cracker smoke mingling with car exhaust, factory emissions, construction dust and crop stubble burning from nearby states turning the winter air into a putrid grey-yellow.

Scientists have also been warning that this year's Diwali celebrations have increased health risks amid crowding at markets ahead of the festival, the cold and the air pollution, which studies have linked to increased coronavirus deaths.

The metropolis has been recording higher-than-usual daily rises in new cases, and reported 7,340 fresh infections late Saturday.

Delhi Chief Minister Arvind Kejriwal is expected to meet with national Home Minister Amit Shah later Sunday to ask for more beds to cope with the spike, local media reported.