The fiercest fires are raging in Tak’s Umphang district, where more than 200 hotspots have been detected.
The mountainous landscape is hampering the efforts of officials and volunteers to stem the progress of the fires.
Officials said many of the forest fires were started by local people, both in Umphang and over the border in Myanmar. They also suspect that locals have been burning the forest to make it easier to gather wild produce such as mushrooms.