Weather-hardened vendors kept selling food amid waist-deep floods swamping southern Thailand on Christmas Day.

A resident opened her stall despite the heavy flooding, with locals wading through the deluge to buy some food in Narathiwat province bordering Malaysia on December 25.

Footage shows rain battering the neighbourhood, spawning severe floods that rendered the roads impassable to vehicles.

Local media reported that thousands were affected by the heavy rain, said to be the most severe the region has seen in 40 years.

Interior Ministry spokesman Traisuree Taisaranakul said 24 districts across the provinces of Narathiwat, Yala, Pattani, Songkhla, and Satun have been worst affected by floods.

While satellite imagery showed that 142 square kilometres were now underwater.

Officials said that flooding has impacted 19,624 households across the region.

Authorities have warned residents in flooded areas to protect themselves against potential hazards including illnesses, electric shocks, and venomous animals lurking in the flood.

Southern Thailand is reaching the climax of its annual monsoon rainy season.