Local media footage showed streets submerged by the muddy deluge and residents taking refuge on rooftops.
Relief teams worked by night to hand out bottled water and snacks and check buildings for damage or casualties.
Thailand’s Department of Disaster Prevention and Mitigation said the water level had reduced on Wednesday morning.
Some rail services in Narathiwat province, which borders Malaysia, had resumed following days of closure due to track subsidence, deputy governor Preecha said.
The kingdom’s rainy season typically brings months of daily deluges but scientists say man-made climate change can make rainfall more intense.
In 2011, widespread flooding killed hundreds and damaged millions of homes around the country.