Schools across Pakistan’s second largest city Lahore closed for the second time in a month on Friday, with the city blanketed in a toxic smog that experts say is putting residents at risk.

Every November, a combination of industrial pollution, burning waste and farm fires in neighboring India fouls the air in Pakistan’s cultural capital, making it one of the world’s most polluted cities.

The Punjab state government has already ordered the closure of thousands of primitive brick kilns that dot the state in order to ease pollution.

But on Friday the Air Quality Index from a monitoring station at the United States’ consulate hit a year-high 451 out of a possible 500, a level considered “hazardous” and where even healthy people are advised to stay indoors.

Punjab Education Minister Murad Raas told Reuters the government was taking necessary measures, including the school holiday. Rights group Amnesty International, however, called the government’s response inadequate, saying Pakistani authorities were playing down the crisis.

According to a 2015 report published by the medical journal Lancet, nearly 22 percent of annual deaths in Pakistan – or more than 310,000 each year - are caused by pollution, most due to air contamination.

“I am personally suffering an eye infection and skin allergies due to smog,” said Zainab Khan, a university student in the city of more than 11 million.

“My classmates also suffered bronchitis, lung infections and other smog related diseases. The government must show seriousness to resolve this problem.”

Sahibzad Khan, Lahore’s chief meteorologist, told Reuters the smog will continue until mid-December.