Emergency crews in Narathiwat province are trying to stop a forest fire spreading towards Sirindhorn Peat Swamp Forest Nature Research and Study Centre, after it came within 40m of the boundary.
The fire has been burning for three days in a village of the province's Sungai Kolok district.
It has destroyed more than 200 rai of agricultural land, rubber plantations, palm trees and fruit orchards belonging to local farmers.
The fire spread quickly to the next district, Tak Bai, covering more than 10 kilometres.
The blaze is now just 30-40 metres away from the swamp research centre — located in the largest remaining freshwater swamp forest in Thailand, which is home to rare fauna and flora.
Occupying 192 square kilometres, the so-called Phru To Daeng swamp forest covers Tak Bai, Sungai Kolok and Sungai Padi districts.
Firemen are trying to prevent the blaze spreading to the swamp after locals lost their battle with it.
Fumes from the fire have affected visibility in Tak Bai district, where more than 60 rai of agricultural land, mostly watermelon plantations, have been destroyed.
Authorities are assessing damage caused by the fire in the two districts.
Last month, wildfire ravaged more than 700 rai of the swamp forest before firemen were able to stop it.