The flooding was brought on by up to 800 millimetres of rain in and around Binh Dinh province on Friday and Saturday, according to the Hydro-Meteorological Forecasting Centre.
"I have never seen such a large-scale flood in Binh Dinh province in the past 30 years" Phan Xuan Hai, director of the province's Committee for Storm and Flood Control, told dpa Friday.
Some waterways were running 2 metres above their normal level, the centre said.
Floodwaters have hit thousands of houses and cut off several areas. Authorities evacuated about 70,000 people, but thousands remain stranded. The military has mobilized helicopters to help.
Flooding in Hoi An, in Quang Nam, province forced thousands of foreign tourists to evacuate, with many navigating the streets of the historic town in small boats.
Authority said water were withdrawing, but very slowly.//DPA