Toxic smog has shrouded the Indian capital as air quality plummeted to hazardous levels after tens of thousands of people set off a multitude of firecrackers to celebrate the major Hindu festival of Diwali.

With schools closed for holidays, many young children stayed indoors to escape the pollution levels that shot up to 681, as reported by the US Embassy on Thursday morning.

India Hindu Festival
People celebrate Diwali in Allahabad, India (Rajesh Kumar Singh/AP)

That is 20 times higher than what is considered safe by the World Health Organisation and could cause serious aggravation of heart or lung diseases.

A government organisation blamed it on a combination of toxic fumes from the burning of stubbles in agricultural fields and firecrackers.

Revellers flouted the Supreme Court order that firecrackers could be exploded only between 8pm and 10pm on the festival night on Wednesday.

India Toxic Air
A thick lawyer of pollution haze hangs a day after Diwali festival, in New Delhi (Manish Swarup/AP)

Rias Ahmed, an auto rickshaw driver, said it was highly unlikely that air pollution was going to decrease in and around the Indian capital.

“I have been driving an auto rickshaw since 1994, for 24 or 25 years, and it has been very difficult due to the high pollution. Sometimes when we clean our nose, it’s all black. When we spit or cough, that’s all black. This is a problem.”

Mohammad Shahid Raza, a young student, said people let off firecrackers until 1am on Thursday in a south Delhi neighbourhood where he lived.

“It was very noisy, and on top of that the pollution level was so high, that when I went outside my house to buy some water, I could see dark clouds, and everything was completely dark. This is not good.”

India Toxic Air
Morning haze envelops the skyline on the outskirts of New Delhi (Altaf Qadri/AP)

Authorities this week tried to reduce dust by sprinkling water in many neighbourhoods and ordering builders to cover construction sites. Coal-based power stations in the Indian capital region have been shut down.

The transport department was checking buses entering the region for valid emission papers and threatening to punish violators.

The government has banned diesel vehicles that are more than 10 years old.

On Wednesday, it banned the entry of diesel-run trucks into New Delhi from November 8-10 to control the pollution levels. Only those bringing food supplies and vegetables are being allowed.

Crop burning peaks in early November as farmers prepare their fields for sowing winter crops, mainly wheat. They have been ignoring government warnings of a penalty, saying they cannot afford to buy harvesting machines.

The Central Pollution Control Board is considering cloud seeding to induce artificial rain if the air is not clearer by next week, the Press Trust of India reported.