The National Centre for Hydro-Meteorological Forecasting said floodwaters on the lower Kon River in Gia Lai were expected to rise above the second warning level over the next 24 hours.
Water levels on the lower Ba River in Dak Lak are forecast to reach between the first and second warning levels, while rivers in Hue, Danang and eastern Gia Lai are expected to fluctuate around the first warning level.
Floodwaters on the Ky Lo River are expected to continue receding to between the first and second warning levels, while the Ve River is forecast to fall below the first warning level.
Authorities warned of a high risk of flooding in low-lying riverside areas and urban centres, as well as flash floods and landslides on steep slopes from Hue to Khanh Hoa.
Flood disaster risks have been classified at Levels 1-2, with potential disruption to waterway transport, aquaculture, agriculture, residential areas and other economic activities.
At the time of the warning, floodwaters on the lower Kon River were fluctuating between the first and second warning levels.
Water levels on major rivers in Hue and from Danang to Khanh Hoa were generally around the first warning level.
The Ky Lo River in Dak Lak was receding but remained above the second warning level, while the Ve River in Quang Ngai was below the second warning level. The Tra Khuc River had already fallen below the first warning level.
At 7 am on November 12, the Bo River in Hue measured 2.4 metres at Phu Oc station, 0.6 metres below the second warning level.
The Huong River reached 1.15 metres at Kim Long station, 0.18 metres above the first warning level.
In Quang Ngai, the Ve River stood at 3.41 metres at Song Ve station, 0.09 metres below the second warning level.
The Kon River in Gia Lai reached 6.38 metres at Thach Hoa station, 0.38 metres above the first warning level.
Meanwhile, the Ky Lo River in Dak Lak measured 9 metres at Ha Bang station, 0.5 metres above the second warning level.
The national weather agency also warned of continued rainfall and heightened risks of flash floods and landslides across central provinces.
Between 10.20 am and 3.20 pm on November 12, rainfall was forecast at 30-40 millimetres in Hue, Danang and Quang Ngai, with some areas receiving more than 90 millimetres.
Gia Lai and Dak Lak were expected to receive 30-60 millimetres, locally exceeding 120 millimetres, while Khanh Hoa could see 10-30 millimetres, with isolated totals above 70 millimetres.
Flash floods in small rivers and streams, along with landslides on steep slopes, could affect numerous communes and wards. The disaster risk level for flash floods, landslides and rain-related ground subsidence was set at Level 1.
The agency warned that such incidents could threaten lives, block roads, damage homes and infrastructure, and disrupt production and economic activities.
Local authorities were urged to inspect vulnerable areas and locations where waterways could become obstructed, and take preventive measures.
Heavy rainfall was recorded across the region between 9 am on November 11 and 9 am on November 12.
Notable totals included 126.2 millimetres at Thuy Yen Reservoir in Hue, 322.8 millimetres at Nuoc Ron Reservoir in Danang and 186.6 millimetres in Ba Nam, Quang Ngai.
Canh Lien in Gia Lai recorded 368.7 millimetres, Son Long in Dak Lak 299.2 millimetres, and the Da Ban Reservoir-Ho Dai catchment area in Khanh Hoa 197.6 millimetres.
Soil moisture models showed that some areas had reached near-saturation levels of more than 85 per cent or were already saturated, increasing the risk of further landslides.