Nepal has ordered schools to close for four days after air pollution climbed to hazardous levels, forcing millions of students to stay home across the country.
Nepal, with a population of 30 million people, is located in the Himalayas between China and India, two of the world's biggest polluters.
Air pollution is a chronic problem in the rapidly growing capital city of Kathmandu and an additional headache for a government struggling to contain the coronavirus pandemic.
Over the weekend, pollution levels hit their highest in the capital since the government began keeping records in 2016, government official Shankar Paudel said.
Education ministry spokesman Deepak Sharma said about eight million students have been affected by the closures.
The 24-hour average level of PM2.5, fine particulate matter that can reach deep into the lungs, was 214 micrograms per cubic metre in the upscale area of Bhaisepati in Kathmandu on Sunday, Department of Environment data showed.
That compares with the government's standard level of 40 micrograms per cubic metre.
Dust from construction works, exhaust from poorly maintained vehicles and smoke from coal-burning brick kilns blend in a murky haze that hangs over the ancient city of four million people, raising the risk of cancer, stroke, asthma and high blood pressure, experts say.
"This also adds to the risk of COVID-19," said Sher Bahadur Pun, a doctor at a tropical and infectious disease hospital in the capital.
Arjun Khadka, 65, who owns a grocery store in Kathmandu, said he experienced itching and burning sensations in the eyes and nose.
"I don't remember this level of pollution in Kathmandu in the past," Khadka said.
People must stay safe indoors and not come out except for emergencies, the health ministry said.
Officials at Nepal's only international airport, in Kathmandu, said poor visibility, which was down to 1000 metres on Monday, widely disrupted flights.