
About 1,000 houses have been flooded in Narathiwat, hard hit by heavy downpours lasting almost a week.
Many roads were impassable and government offices and houses under water. All train service has been suspended due to washed out tracks.
Flash floods from the Sankalakhiri mountain range in Sukhirin district poured into the main rivers and waterways, causing overflowing in 13 districts.
More than 3,000 homes have been affected while eight districts suffered the most disruption.
A stretch of railroad was damaged and all train services halted while maintenance crews repaired the track.
Rescue workers were ready to respond to any emergency in five southern provinces.
The local weather department warned residents in disasterprone areas to beware of possible flash floods, as the northeastern monsoon prevails over the Gulf of Thailand and the southern region.
In Phattalung, five lowlying districts were under about one metre of water. Some 30 households took temporary shelter in roadside camps.
In Yala's Raman district, the Saiburi River broke its banks, flooding low lying areas along the river and forcing residents to move their belongings to higher ground. Some roads are submerged under two metres of floodwater and villagers have to use small boats to get around.
Yala declared Raman, Yaha and Kronpinang districts as disaster zones as almost 100 villages were flooded, affecting more than 7,600 residents.
Military units are helping to transfer locals to higher ground where communities were cut off.