The city's Civil Defence Command issued the highest level-three alert for the Tich and Bui rivers and a level-two alert for the Day and Nhue rivers.
At 2.40am on September 17, the Tich River at Kim Quan reached 8.43 metres, 0.03 metres above the level-three threshold, prompting an alert for several areas along the river.
The Day River at Ba Tha reached 6.52 metres at 5am, 0.02 metres above the level-two threshold, while the Nhue River at Dong Quan rose to 4.42 metres at 5.50am, also 0.02 metres above the level-two mark.
A level-three alert had already been issued for the Bui River on September 16, covering several communes including Xuan Mai, Phu Nghia and Tran Phu.
Hundreds of soldiers, police officers, militia members and residents braved the rain to reinforce vulnerable sections of the more than one-kilometre Bui Hai dyke in Xuan Mai and Tran Phu.
The city ordered local civil defence units and relevant agencies in affected areas to implement measures required under the respective flood alert levels.
The Northern Regional Hydro-Meteorological Centre said water levels on the Nhue and Day rivers were continuing to rise.
The Nhue River at Dong Quan is forecast to reach 4.65 metres by 8am on September 18, just 0.05 metres below the level-three threshold. The Day River at Ba Tha is expected to reach 6.75 metres by 7am, 0.25 metres above the level-two threshold.
High river levels could flood low-lying and riverside areas and mid-river islets, while increasing the risk of landslides and threatening vulnerable dykes, bridges, culverts and riverside roads.