(Bloomberg) -- Raging forest fires in northern Thailand are threatening to worsen the country’s air pollution, which has sent nearly two million people to hospitals with respiratory illnesses since the beginning of the year. 

Prime Minister Prayuth Chan-Ocha on Thursday ordered urgent steps to put out forest fires in Nakhon Nayok province in the east of capital Bangkok and those in the country’s northern region including popular tourist destination Chiang Mai and Chiang Rai, according to government spokesman Anucha Burapachasri. 

Firefighters and other officials have been deployed to monitor the affected areas, as burning of farmlands and illegal foraging occur during this time of the year, Anucha said in a statement on Thursday.

A mountain known as Khao Laem in Nakhon Nayok that was engulfed in flames since Wednesday has been brought under control, the government said late on Thursday. Several wildfires are also reported from protected forests in Thailand’s north, with several hotspots across the borders in neighboring Myanmar and Laos, a satellite heat map by a Thai space agency showed. 

The wildfires are the latest cause for the worsening air quality in Thailand that’s pushed levels of particulate dust particles known as PM 2.5 in some areas past unhealthy threshold into a hazardous zone. 

Bangkok and other Thai cities have grappled with poor air quality in recent years, with pollution tending to get worse in the dry season around December to February due largely to agricultural burning in Thailand and neighboring countries, and vehicular emission.

Prayuth urged the Association of Southeast Asian Nations on Thursday to take steps to tackle the trans-boundary haze situation that stems mainly from hotspots across the region, Anucha said in a separate statement.

READ: Bangkok Urges Work From Home as City’s Air Pollution Worsens (1)

Chiang Mai was ranked as the world’s most polluted city by air quality monitor IQAir earlier on Thursday, with a “very unhealthy” PM2.5 concentration reading. Its neighboring province Chiang Rai had a “hazardous” reading for most of the last seven days, IQAir data showed. 

The Ministry of Public Health said eight provinces in Thailand’s north were being monitored for dangerous levels of air pollution, which is expected to last until early April and normalize in May.

Patients with air pollution-related diseases in Thai hospitals have more than spiked to more than 1.73 million between Jan. 1 and March 19 this year, according to Opas Karnkawinpong, the ministry’s permanent-secretary. Thais are urged to stay indoor as much as possible or wear respirators when outside, he said.

(Updates with prime minister’s comment in seventh paragraph. An earlier version of the story corrected location of forest fire in fourth paragraph.)

©2023 Bloomberg L.P.