Chiang Mai declared four more areas as wildfire crisis zones on Tuesday amid growing concerns over the North's haze pollution problem.
The four areas cover 10 villages in Mae Taeng district and six villages in Phrao district, said Chiang Mai governor Nirat Pongsitthaworn.
The governor said these new wildfire crisis zones cover Srilanna National Park, Doi Luang Chiang Dao and Huai Tueng Thao, which are among the province's popular tourist destinations.
He said seven other areas were declared wildfire crisis zones earlier, adding that these areas covered villages in Hang Dong, Muang, Mae Taeng, Phrao, Chaing Dao and Mae Rim districts.
Since March 23, the average number of hotspots reported daily is between 200 and 600, while the air pollution situation is worsening, Mr Nirat said.
More than 700,000 N95 masks have been given away to people to protect themselves as much as possible from serious air pollution, the governor said.
"Most of these new wildfires are man-made," he said. "Please drop the old-fashioned belief that burning up a forest will yield more wild products such as phak wan and het thop."
As artificial rain-making operations had seemed unsuccessful, the province could only pin its hopes on natural rain, which usually comes before the Songkran festival each year, he said.
As those who burn forest areas expect the rain to arrive soon, they tend to try and set more fires in northern provinces, said Bannarot Buakhli, an adviser to Sapha Lom Hai Chai Chiang Mai (Chiang Mai's council of breath).
He said people burn forest land because they expected edible wild products to regrow better after fire and rain.
Chiang Mai's wildfire and haze prevention and resolution centre said the maximum level of hazardous PM2.5 dust on Tuesday was up 795 microgrammes per cubic metre (µg/m³) in Suan Dok community in tambon Doi Suthep in Muang district.
In neighbouring Chiang Rai, additional firefighters have been deployed in the province to reinforce existing teams, who have had 15 members injured over the past few days while fighting fires.
In the northeastern province of Nakhon Ratchasima, up to 695 hotspots were detected in the past three months, while 16 major wildfires during the past five months damaged up to 173 rai of forest land, mostly in Thap Lan National Park.