They are forecast to continue rising quickly on Thursday, possibly triggering severe flooding in large parts of Quang Ngai Town, the capital, and several districts.
The release of water by local hydropower dams is worsening the situation.
Dak Drinh hydropower plant discharged up to 1,680 cubic meters of water a second on Wednesday and Nuoc Trong, the largest irrigation and hydroelectricity project in the central region, discharged 1,100 cubic meters.
Authorities hurriedly evacuated people living in low-lying areas and made emergency announcements about the water discharge via loudspeakers to warn local residents.
In Quang Nam Province, home to ancient town Hoi An, the water level in the Vu Gia River reached 9.41 meters by early morning Thursday, 0.41 meters above danger level 3, according to the National Center for Hydro-Meteorological Forecasting, which warned rivers in the province would rise quickly in the next few hours.
Dak Mi 4 hydropower plant plans to discharge up to 11,400 cubic meters a second and the Vu Gia River is expected to rise to 11.2 meters, surpassing the historic flood level in 2009.
Dak Mi 4 hydropower plant in Quang Nam Province discharges water on October 13, 2020. Photo by VnExpress/Dac Thanh.
Nguyen Huu Vu, a local official, said authorities have evacuated over 4,000 families living along the river.
If the hydropower plant discharges over 5,000 cubic meters per second, 120,000 houses would be submerged under 0.5-1.5 meters of water, Vu said.
The National Hydro-Meteorological Forecasting Center said on Wednesday that Quang Nam could face severe flooding in the next one or two days.
Deputy Prime Minister Trinh Dinh Dung instructed provincial authorities to evacuate people from areas threatened by landslides and ensure the safety of reservoirs and hydropower plants.
The central region, including Quang Nam, was hit by prolonged heavy rains, historic flooding and deadly landslides for three weeks from October 6 that caused at least 130 deaths.
The flooding left 290,000 houses submerged and large swathes of agricultural land inundated, killed livestock and caused damage the government said was "the worst in the last five years."