Nine provinces along Thailand's southern tail have been hit by unseasonal rains for nearly a week, with the resort islands of Samui and Phangan deluged, leaving thousands of tourists stranded or delayed.
Eight people have been killed and at least 120,000 households have been affected by the flooding across the south, the Interior Ministry said, where waters have turned roads into rivers and upended rail tracks.
Authorities fear worse may be to come.
The Thai Meteorological Department warned residents and visitors to the south of possible "heavy rain and flash floods" with downpours expected to continue for two more days.
Photos circulating on social media showed cars and motorcyclists plying through muddy, waist-high waters.
A smattering of foreign tourists on Samui took advantage of the flooded streets, drawing bemused looks from locals as they bobbed along in inflatable tubes sipping beers.
Tuula Fitzpatrick, the owner of Moby Dick guesthouse near Samui's main party strip, said the flooding was the worst to hit the island in over a decade.
"I've been living here for 12 years and I've never seen it so bad... It was scary. Some of my staff couldn't come to work," she told AFP.
The island, a stalwart of Thailand's cash-cow tourism industry, is a magnet for foreign visitors drawn by the promise of winter sun.
But under menacing skies tourists stayed inside hotels, while others checked out early or cancelled bookings, according to a Thai tourism official on the island.
Planes, trains stopped
The worst flooding struck Nakhon Si Thammarat province on the mainland, where waters reached the roof-tops in some parts, closed the regional airport, cut the trainline and made roads impassable.
"The flood waters have hit the tracks and in some places the track was washed away," said Thanongsak Kongprasert, deputy governor of the State Railway of Thailand.
Junta chief Prayut Chan-O-Cha briefly visited the southernmost province of Narathiwat to distribute flood relief.
Across the border in northern Malaysia more than 15,000 people remained stranded in relief centres after days of tropical downpours as thousands more headed home to survey the damage wreaked by the floods.
"The weatherman has predicted no more heavy rain. More relief centres are being closed but we remain on alert," Amir Sarifudin, Terengganu state civil department force deputy director, told AFP.
But frustration mounted among those stuck in relief centres as evacuees complained of their inability to work and provide for their families.
"I usually earn about 50 ringgit ($11) daily. Now I only have 15 ringgit in my pocket for my family of four," said Mohamad Zain Sapein, a labourer from northern Kelantan state.
The rains are unusually heavy for this time of year, with the region normally experiencing a cooler, dry period from early November through January -- the three-month long peak tourist season.