A bushfire ravages Doi Suthep-Pui National Park in Chiang Mai's Hang Dong district on Wednesday night. Local officials and soldiers spent more than 14 hours bringing it under control. (Photo courtesy Chiang Mai Volunteer Drone Team)

Prime Minister Prayut Chan-o-cha on Thursday expressed concern over massive damage caused by a bushfire in Doi Suthep-Pui National Park in Chiang Mai, which also sent air pollution in the northern province to record highs.

Although the blaze -- which broke out on Wednesday evening -- has been brought under control, the damage it left behind is extensive, Chiang Mai governor, Charoenrit Sanguansat, said on Thursday.

He added that the bushfire also sent PM2.5 levels in the area to "record levels" of around 1,000 microgrammes per cubic metre (µg/m³), 20 times above levels considered safe by the Pollution Control Department (PCD).

Mr Charoenrit said that almost 500 local officials and soldiers from the 3rd Army Region were called in to fight the blaze.

They spent more than 14 hours bringing the bushfire under control, he said.

In Bangkok, government spokeswoman Narumon Pinyosinwat said the prime minister was gravely concerned by the fire in Doi Suthep-Pui National Park, and ordered related agencies under the Interior Ministry to work with the Royal Thai Army to put out the rest of the blaze. He also ordered helicopters to assist with the mission.

"[Gen Prayut's] primary concern is the health of the elderly and children, and he asked them to avoid going outside because of the smoke," she said.

Chiang Mai was not the only northern province plagued with air pollution issues, with many others registering PM2.5 levels above 50µg/m³.

The PCD's latest PM2.5 dust index also revealed severely unhealthy levels of air pollution in Chiang Rai, Mae Hong Son and Nan on Thursday. Unhealthy readings were also reported by air quality monitoring stations in Lampang, Lamphun, Phrae, Phayao, Tak and Kamphaeng Phet.

Pralong Dumrongthai, PCD director-general, said based on the most recent satellite imagery, the number of hotspots in the North is likely to decrease. At present, there are 377 and 364 hotspots in and around Chiang Mai and Mae Hong Son, respectively.

Mr Pralong said the air pollution in the North can partly be blamed on fires across the border, and the government is working with Myanmar to help address the issue.

Meanwhile in Phayao, villagers and park officials took 15 hours to put out a bushfire in Phu Sang National Park, said park chief Banthom Somsuwan on Thursday.