The flooding, which is roof-high in some areas, has affected more than 700,000 people since it started a week ago, the Interior Ministry said in a statement.
At least 12 people have died, according to counts from the ministry and local officials, as waters turn roads into rivers and rip away stretches of rail track.
The downpour is expected to persist for at least two more days, according to the Meteorological Department, which warned of flash floods in eight of the hardest-hit provinces.
"The situation is very bad today and tomorrow. It's still raining heavily," Junjuda Pornsri, a metrological official, told AFP.
The capital of Nakhon Si Thammarat province, which has shuttered its airport because of the weather, saw a record 162.1 millimetres (6.4 inches) of rain on Friday night, she added.
The downpour is unusually strong for this time of year in Thailand, which normally sees a three-month long stretch of relatively dry and cool weather from November through to January.
It is high season for tourists who flock to the kingdom's island resorts, powering a crucial sector of the economy.
But the deluge has already disrupted beach holidays in several traveller hotspots, including the popular islands of Samui and Phangan.
Hundreds of tourists have had their flights delayed, while train and bus services on the mainland have also been suspended in flood-hit areas.
Yet some travellers are refusing to let the storm stop the fun, with photos circulating on social media of tourists coasting through flooded streets on pool floats.
"Some tourists are enjoying the flooding, they're taking pictures and going swimming," said Nongyao Jirundorn, a tourism official on Samui island.
Neighbouring Malaysia was also hit by severe flooding earlier this week, with thousands stranded in relief centres in two northeastern states.
But by Saturday, the number of evacuees in Kelantan and Terengganu had dropped to about 12,500, from almost 23,000 Wednesday, as weather conditions improved and authorities forecast less rainfall over the weekend.
Published : January 07, 2017
By : Agence France-Presse