Pollution levels have spiked to hazardous levels in New Delhi due to the widespread use of firecrackers, despite a court restricting their use during Diwali festivities.

The Supreme Court had limited setting off firecrackers to two hours on Diwali, the Hindu festival of lights, on Wednesday night. But tens of thousands of revellers continued to burst firecrackers till late, violating the order and contributing to a haze over the capital.

The levels of suspended particles smaller than 2.5 micrometres (PM2.5) hovered between 400 and 999 micrograms per cubic metre, the maximum reading possible, at air quality monitoring stations early Thursday.

The readings were 20 to 40 times over the safe limit set by the World Health Organization, which recommends that people should not be exposed to PM2.5 levels of over 25 micrograms in any 24-hour period, as the small particles can get deep into the lungs and even reach the bloodstream.

The overall Air Quality Index was recorded at 356, which falls in the "very poor" category, according to the Central Pollution Control Board.

Domestic media reported that the air quality had begun to deteriorate from 7 pm (1330 GMT) on Wednesday evening, when it rose from 281 to 296 three hours later.

Last month, the Supreme Court imposed strict curbs on fireworks, such as allowing the sale of only "green crackers" that have low emissions as well as "community bursting" of firecrackers in designated areas.

But police were unable to stop the blatant flouting of the orders.

Violations were reported from almost all areas in the city, raising questions on the administration enforcing the restrictions.

Delhi has long been grappling with air pollution that usually spikes in October-November, with crop stubble burning by farmers and Diwali firecrackers adding to emissions from heavy traffic, industry and the burning of garbage and fuel, among other factors.

Several cities, particularly in northern India, also recorded dangerous levels of pollution post Diwali, the CPCB data showed.

Many people went online to express anger over the violations of the court orders and the inability of the police to take action.

Others said it was unfair to curtail the celebrations as fireworks were not responsible for the pollution, blaming crop burning, dust from construction sites and low wind speeds for the pollution levels.

A metropolis with a population of more than 20 million people, New Delhi, has been ranked among the worst-polluted cities in the world in recent years.

Authorities have launched a 10-day "Clean Air Campaign" in the city until November 10 to monitor polluting activities and improve conditions, but the drive has not proved effective in checking the worsening air quality.