An overnight downpour left parts of Khon Kaen's Muang district under water on Monday, with the weather forecast for three more days of heavy rain in Khon Kaen and 10 other northeastern provinces.
Motorists in downtown Khon Kaen had to negotiate still-rising water levels on many roads during the morning rush hours.
Khon Kaen City's Facebook account carried a warning for drivers to avoid the flooded areas if possible.
The weather office said more heavy rain was expected in Khon Kaen and 10 other northeastern provinces until Thursday.
Warnings of possible flooding were also issued for Bung Kan, Chaiyaphum, Kalasin, Loei, Maha Sarakham, Nakhon Phanom, Nong Bua Lamphu, Nong Khai, Sakon Nakhon and Udon Thani.