While the skies were unusually clear above the notoriously polluted Beijing as U.S. President Donald Trump began his state visit Tuesday, the air quality in the capital of another Asian superpower has plummeted.

India's capital Delhi has been shrouded by smog in recent days. The U.S. embassy in the city, which routinely , recorded the air quality index (AQI) to be at 1,010 at 4 p.m. local time (5:30 a.m. ET) on Wednesday. According to the embassy's website, a score of between 301 and 500 is deemed "hazardous."

"Delhi has become a gas chamber," tweeted Delhi Chief Minister Arvind Kejriwal on Tuesday.

The air pollution in Delhi is particularly severe at this time of year as nearby farmers burn crop stubble to clear their fields. This, in combination with current weather conditions of cool temperatures and low wind speeds, means that smog can fester in the city.

"It's a public health emergency," said Dr. Krishnan Kumar Aggarwal, cardiologist and president of the Indian Medical Association. He advised people to limit physical activities when pollution levels were particularly high.

The government has undertaken a series of measures to help residents cope with the pollution levels. As of Wednesday, schools were closed. Officials are reportedly considering the implementation of traffic restrictions. Earlier this year, the Supreme Court banned the sale of firecrackers in Delhi ahead of the Hindu festival of Diwali on October 19.

Airtel, the leading sponsor of the Delhi half marathon scheduled for November 19, has voiced concerns about the race going ahead. "Air pollution poses serious health risks and it is important that these concerns are addressed urgently and appropriately by the authorities for Airtel to continue associating with the event next year and beyond," said the company in a statement earlier this week.

Delhi, home to nearly 19 million people, is among the world's most polluted cities according to the World Health Organization.