Authorities in Gia Lai Province said prolonged torrential rain since November 18 sent river levels surging, inundating Quy Nhon and nearby areas.
Gia Lai Party Secretary Thai Dai Ngoc instructed rescue teams to reach isolated, deeply flooded zones by any means necessary.
Rescue crews used small boats to ferry stranded residents in Quy Nhon Bac Ward to safety.
In Dak Lak, the Song Ba Ha Hydropower Plant discharged 16,100 cubic metres of water per second on November 19, affecting downstream communities.
According to the National Centre for Hydro Meteorological Forecasting, the Ba River stood at 40.99 metres at Cuong Son at 3.30 am on November 20, which was 6.49 metres above alarm level three and 1.09 metres higher than the 1993 record. At Phu Lam, levels reached 5.36 metres, topping alarm level three by 1.66 metres and exceeding the 1993 peak by 0.15 metres.
Flooding has destroyed eight houses, submerged 23,000 others and left 1,123 households isolated in Dak Lak. Authorities have evacuated 7,765 high-risk households, but rising water levels mean the number of inundated homes is likely to grow.
Van Thinh, a resident of Tuy Hoa Ward, said he had never seen floodwaters rise so quickly. “I live in a high area, and in 40 years I have never had to flee a flood, but this time half a metre of water entered my house and damaged many belongings,” he said.
Overnight, police in Tay Hoa Commune waded through fast-flowing water to reach isolated and deeply flooded areas to move residents to safety.
Khanh Hoa authorities said flooding has submerged nearly 9,000 homes under 0.3-0.7 metres of water. At 3.30 am on November 20, water on the Dinh River at Ninh Hoa reached 6.62 metres, exceeding alarm level three by 0.92 metres and surpassing the 1986 record by 0.04 metres.
Residents in Khanh Hoa's Nam Nha Trang Ward edged their way through deep water on Vo Nguyen Giap Street.
Rescue teams evacuated an elderly woman trapped in a flooded, isolated area of Hoa Thang Ward.