A heavy monsoon season has flooded 27 provinces in Thailand, killing nine and forcing evacuations in at least nine districts.
Authorities said floodwater would not reach the central industrial areas or Bangkok, as it did in 2011 when it caused big disruption to supply chains, but urged residents to evacuate.
Thousands fled their homes on army lorries with food and water in plastic bags.
"The water came too fast, the dam was damaged by the floodwater. We used sand bags to mend it, but it collapsed two days later," said Virat Naewchan, mayor of Srimahaphot municipal district in Prachinburi province.
Prachinburi was declared one of the worst hit in the country. Streets have been turned into waterways and cars replaced by boats. Many of the residents are too scared to leave their homes.
Dara Noijaisin, 63, lives in a home surrounded by water. With four grandchildren to take care of, she said that evacuating the whole family would be too dangerous as they have nowhere to go.
"It's OK if it doesn't rain, but I'm worried and scared it will rain again," she said.
So far, about 1.5 million people from 420,000 households have been affected.
Cambodia and China
Elsewhere in Cambodia, floods have killed at least 20 and left more than 33,000 families affected, according to the National Committee for Disaster Management.
Meanwhile, tropical storm Wutip has upgraded to a severe tropical cyclone and is expected to bring heavy rain and gale to south China's Hainan province before making its way to central Vietnam.
It is expected to become a typhoon before making impact on Monday.
The storm will cause torrential downpours not only in Vietnam, but across the region, so the flooding is likely to get worse.
The Chinese province's meteorological department on Saturday morning launched a grade three emergency response alert.
The meteorological department have already warned local fishermen operating in the central area of South China Sea to dodge the storm center and avoid outdoor activities until further notice.