At least 745 people have died in flooding in Thailand, Cambodia, Vietnam, Laos and the Philippines since July, the Regional Office for Asia and the Pacific said.
Thailand has been hit the hardest, with 315 people killed in that time frame, officials said.
Monsoon rains across Thailand have affected millions of people in 61 of its provinces, the country's Flood Relief Operation Command reported.
Cambodia, meanwhile, reported 247 dead since July.
- CNN's Kocha Olarn contributed to this report.