A group of nine tourists from Phuket were at a camping resort near the Wang Lung Waterfall in Phrom Khiri District when heavy rainfall in the nearby mountain range triggered a sudden flash flood.
Despite warnings from the business owner about the rising water levels, the tourists continued to stay at the waterfall.
When the water changed colour, a second warning was issued, but three of the tourists were soon caught by the fast-moving floodwaters.
Locals were able to rescue one of them, Ms Orrawan Kunok, 42, who was rushed to Phrom Khiri Hospital.
However, the other two tourists, Wilawan Boonnum, 48, and Upatham Tha-ue, 43, both residents of Phuket, were swept away. Their bodies were found later that evening at around 6pm.
Ms Wilawan and Mr Upatham were the only two people to die in flooding in Nakhon Sri Thammarat on Friday.
In Betong district of Yala, Koder Luebaji, 66, was swept away on Friday evening when his house, located on a canal bank, collapsed during heavy rain. His body was later recovered. Six of his family members managed to escape and seek shelter with relatives, reports the Bangkok Post.