A quarter of Thailand has been inundated in the worst flooding in half a century, killing 17 people, while 20 people have died in neighbouring Cambodia.
Rising waters hit the homes and livelihoods of nearly 1 million people and threatened to swamp parts of the capital.
Victims were swept to their deaths as heavy rains swelled rivers and reservoirs, sending water gushing through the streets and immersing huge swathes of farmland.
Thailand's Disaster Prevention and Mitigation Department says more than 800,000 people, or about 285,000 households, have been directly affected.
Four people died in Buriram, in eastern Thailand, as waters gushed through the streets, while the death toll in Nakhon Ratchasima has risen to four.
Residents in Nakhon Ratchasima, where 30 of 32 districts are already under water, have been told to evacuate or move to higher ground after a local reservoir burst its banks.
The central provinces of Rayong and Trat have both reported one casualty, while a further two people were killed in Lopburi.
Rescue teams have helped evacuate stranded people by boat, as homes and huge swathes of farmland have been deluged.
The area to the north-east of Bangkok is worst affected after twice the amount of rain compared to this time last year.
Interior minister Chavarat Charnvirakul said the government will double the emergency fund available to provinces for flood relief.
Prime Minister Abhisit Vejjajiva has visited affected areas and offered aid to people whose homes and farms have been flooded.
He says Nakhon Ratchasima is suffering its worst flooding in 40 to 50 years.