Schools closed, roads and railways submerged and people forced onto their roofs amid torrential rain.
The province of Narathiwat in the country’s far south near the border with Malaysia was most seriously affected, with some districts submerged for days, according to broadcaster Thai PBS.
It said that “scores of people” had requested assistance and some were sitting on the roofs of their flooded homes.
At least a dozen schools in the provinces of Narathiwat and neighbouring Yala have been forced to close, while footage from the region showed homes and shops inundated with water.
Days of torrential rain have also caused problems at sea, with at least seven boats sunk in the Gulf of Thailand and Andaman Sea since Friday.
The kingdom’s state railway company said track subsidence meant that trains heading south to Malaysia were stopping at Yala, 100km (62 miles) away from the border.
Authorities have warned residents in the provinces to be ready to evacuate if the floods get worse.
Serious floods in the region in December last year killed at least three people.