Flood peaks on smaller rivers and the upper reaches of the Thao, Chay, Lo, Cau and Thuong rivers are expected to reach warning levels 1 and 2, with some locations exceeding level 2.
The National Centre for Hydro-Meteorological Forecasting (NCHMF) warned that river flooding could disrupt inland water transport, aquaculture, agriculture and other economic activities.
Northern Vietnam is forecast to receive 40-100 mm of rain through Friday, with isolated areas seeing more than 200 mm.
Thanh Hoa and Nghe An are expected to receive 30-70 mm, with isolated totals exceeding 150 mm, while scattered showers and thunderstorms are forecast for central and southern regions.
The weather agency warned that heavy rain could trigger flash floods, landslides and urban flooding, particularly in mountainous and midland areas where soil is already saturated after recent rainfall.