Torrential rain has continued to pound much of the South, killing one man in a road accident and affecting more than 2,000 residents in Phatthalung.
Up to 69 villages in five of the province's districts are inundated, with about 2,000 householders declared flood victims, officials said on Wednesday.
Muang, Khuan Khanun and Sri Nakharin districts were hardest hit by overnight downpours and mountain runoff from the Banthat mountain range.
The heavy rain lashed residential areas until late Wednesday morning.
In Ban Tha Khae of Muang district, a car skidded off the Asia Highway and crashed into a tree as it was heading to Bang Kaew district.
Rescuers rushed to the scene to help the driver, later identified as Piya Songsaeng, a resident of Bang Kaew district. However, the 40-year-old construction businessman died at the scene of the accident.
Police believed Piya lost control of his vehicle due to the heavy rainfall.
According to the authorities floodwater swept across several sections of the Asia Highway and flooded nearby areas, with the water one metre deep in some locations.
In Sri Nakharin district, rain also saw a 500-metre section of Phetkasem Road, which connects Phatthalung and Trang, under water.
Sri Nakharin Hospital was affected by flooding which hit the facility in the early hours.
Water from Phatthalung is also compounding flooding in neighbouring Trang province.
Many villages in tambons Chong, Lamo, Na Yong Nuea and Na Muen Si in Na Yong district of Trang were hit by flash floods, assistant district chief Manit Thachin said on Wednesday.
Officials scrambled to help residents, fearing another deluge, move their belongings to higher ground.
Residents in Na Yong, Muang, Yan Ta Khao and Palian districts, were also bracing for mudslides as floodwaters continued to rise on Wednesday.
Flooding also affected residents in Ban Sapom in Narathiwat's Tak Bai district. A 55-year-old resident, Hamatnu Sulong, said the floods were made worse by the poorly-built water drainage system in his neighbourhood. More downpours were forecast in many areas of the South.