With widespread rain already causing problems provincial authorities are moving into flood-control mode with forecasters warning of more to come on Friday and through the weekend.
The Disaster Prevention and Mitigation Department has warned people living near mountains to watch out for forest runoff if the rain continues to pound their area.
Khon Kaen Municipality has distributed sandbags to homes for use as floodwalls, as workers continue draining water from the business area. The Muang district has been deluged with rain since the weekend.
Khon Kaen mayor Theerasak Teekayuphan said workgangs would be stationed on Mittaphap Road ready to tackle any sign of flooding because it was a key road linking with other provinces in the northeastern region.
Steady rain was falling in many northeastern provinces on Thursday afternoon and into the evening.
One of the hardest-hit areas in the northeast so far has been Muang district in Nakhon Phanom, where a five-hour downpour starting shortly after midnight flooded the municipality with water up to 50 centimetres deep, damaging several vehicles.
The meteorological office in Nakhon Phanom said 150 millimetres of rain fell, the heaviest fall in the province over the last decade.
The Nakhon Phanom Municipality has installed more pumps to speed up drainage of water into the Mekong River.
Disaster mitigation offices in provinces where heavy rain is anticipated have been put on alert and told to prepare to help people affected by flooding
Other provinces hit by floods on Thursday included Lampang, Sukhothai, Phichit and Ayutthaya.
Somporn Kitket, 74, a farmer in Sena district of Ayutthaya, said the floods had come early this year. Her village was normally flooded from August to early September, not in May.
"The floodwater could be here for a long time this year," she said.
The Meteorological Department issued a new warning at 5pm forecasting heavy rainfall in 24 provinces including Greater Bangkok, Chiang Mai, Chiang Rai, Sukhothai, Nakhon Ratchasima and Ubon Ratchathani.