"The fire ignited about 15 kilometres from Maechan Hospital," officials said, saying they are monitoring the blaze around the clock.
Maechan Hospital is equipped with air purifiers to ensure the health of patients and staff, and is prepared to transfer patients to other hospitals if necessary, officials said.
Provincial officials also told residents of the district they are prepared to handle forest fires and PM2.5 air pollution. PM2.5 refers to fine dust in the air. It is linked to early death from heart or lung ailments.
The Doi Jorakae Mountain blaze started at about 8.30pm on Wednesday, according to a post on the "Doctor Kluay" Facebook page.
Firefighters, community leaders and volunteers arrived at the scene to extinguish the blaze at about 9.50pm, the page said.
It said the fire was under control by 6am on Thursday.
PM2.5 readings in Chiang Rai's Muang district surged to 159 milligrams per cubic metre on Thursday, according to the Pollution Control Department.
Thailand’s safe limit is 50 milligrams per cubic metre.