High tides could exacerbate flooding in Pattani after the municipality was inundated by water overflowing the banks of the river.
Most areas in Muang district have been underwater since Saturday, when a large volume of water released from Bang Lang dam in Yala's Bannang Satar district burst the banks of the Pattani River in the municipality.
Several roads in the town centre were flooded despite machines pumping floodwater back to the river around the clock.
Pattani mayor Pitak Korkiatpitak warned residents on Sunday the high tide in the Gulf of Thailand could raise the water level further still.
The municipality issued a warning on Friday for people in the town and other riverside locations to prepare for the arrival of a water surge from the dam, which increased its outflow to prevent the structure from damage due to overcapacity.
It released another alert on Sunday advising people to move essential items to higher ground, but otherwise stay at home.
Pattani governor Rachit Sudphum on Saturday declared the entire province a disaster area after all districts were submerged, with Muang district hit hardest.
"Flooding started at dawn yesterday (Saturday) and it continues to rise," town resident Sudarat Likittaweechok told Channel 7.
Pattani is the province most devastated by heavy rains that pounded southernmost provinces along the Gulf of Thailand for almost a week, virtually non-stop.
The Disaster Prevention and Mitigation Department reported two people in Yala and one in Songkhla had drowned and almost 60,000 houses in the four provinces of Narathiwat, Pattani, Songkhla and Yala were affected.