Top Asian finance ministers and central bankers are due to have a summit in northern Thailand this week, and they’ll need pollution masks if they want to avoid breathing toxic air.

Wildfires and crop burning are blanketing the region with smog, prompting Thailand’s junta leader Prayuth Chan-Ocha to fly to Chiang Mai -- the area’s tourist hot-spot -- early Tuesday to review the crisis. The city’s air quality index was 379 as he visited, the worst major urban reading globally and a level that’s hazardous, according to IQAir AirVisual pollution data.

The air was classed as unhealthy in nearby Chiang Rai, where finance ministry officials and central bankers from Southeast Asian nations as well as China, Japan and South Korea will meet from Tuesday through Friday. The Bank of Thailand has said it will hand out pollution masks to media covering the event.

Thai authorities blame crop burning to clear farmland, as well as wildfires in mountainous forests amid a drought and searing heat. Chiang Mai has set up a so-called safe zone for residents in a convention center, while a university in Chiang Rai canceled classes on Monday and Tuesday.

"The haze usually comes and goes within a week or two, but it’s been persistent this time -- it’s the worst so far," Khuanchai Supparatpinyo, the director of Chiang Mai University’s Research Institute for Health Sciences, said in an interview. "This can be quite dangerous, and pose health risks."

Northern Thailand is a popular destination for visitors during the traditional Thai new year festival in mid-April but the smog is likely to make some holidaymakers think twice.

At the start of 2019, the military government was rattled by a second year of spiking seasonal air pollution in Bangkok, exacerbated by traffic fumes, industrial emissions and construction dust.

So far the episodes of smog haven’t damaged tourism but worsening haze could pose a challenge for an industry that’s key to economic growth.