The air quality index, or AQI, hit 980 at 4:30 a.m. Thursday, according to website AirVisual, which monitors air pollution around the world. The levels surged as people violated an order of the Supreme Court and burst firecrackers before and after a two-hour window set for the purpose. Readings below 50 are considered safe, while anything above 300 is considered hazardous.

The air quality in the morning was just about as bad as it was in 2017 a day after Diwali, when levels exceeded 1,000, roughly ten times worse than the air pollution in Beijing. The levels on Thursday afternoon came down from their peak, with the gauge reading a “very unhealthy” 244 as of 2:30 p.m. The smog last year led the capital’s chief minister to declare his city had become a “gas chamber.”

Toxic air is estimated to kill more than 1 million Indians each year, according to the nonprofit Health Effects Institute.

Read More: World’s Fastest Growing Economy Has the World’s Most Toxic Air

New Delhi was ranked the most polluted city in the world on Thursday, according to AirVisual’s global rankings. Lahore in Pakistan was at second place with AQI at 273 as of 8 a.m. local time. By comparison, New York had readings of just 29 as of 10 p.m. on Wednesday local time.

With different air quality monitors showing varied readings across the capital, it was still clear that New Delhi’s air was the worst in the world. Levels of dangerous PM 2.5 — the fine, inhalable particles that lodge deep in the lungs, where they can enter the bloodstream — were pushing close to 1,400 in some parts of the Indian capital early on Thursday morning, according to a website run by the Delhi Pollution Control Committee, a government agency.

Burning Crops

Delhi’s air pollution is a toxic mix of vehicular exhaust, smoke from burning crops in the nearby states of Punjab and Haryana, road dust and billowing sand from thousands of construction sites. The pollution is intensified by winter weather patterns and hemmed in by the towering Himalayas to the north.

Severe air pollution — which has been linked to serious ailments including lung cancer and heart disease — affects dozens of cities across South Asia.

Read More: Why Winter Brings Deadly Smog to India’s Capital

Nearby Lahore, over the border in the Pakistani province of Punjab, has been one of the worst affected in recent weeks as agricultural crop burning intensified. Afghanistan’s Kabul and Nepal’s Kathmandu have also been near the top of the pollution rankings.

India alone, according to the World Health Organization’s 2016 rankings, accounted for the world’s 10 most-polluted cities as measured by PM 2.5.

The Lancet estimates that 6.5 million people die annually around the world because of air pollution, mostly in India and China. DM