According to the National Centre for Hydro-Meteorological Forecasting, the depression's centre was over the southern Gulf of Tonkin at 4 pm on August 25.
Winds near its centre reached level 7, or 50-61 kph, with gusts of level 9. The system was moving east at around 10 kph.
By 4 pm on August 26, the depression is forecast to turn northeast while maintaining a speed of around 10 kph.
It is expected to move over the northern Leizhou Peninsula in China and weaken into a low-pressure area, with winds below level 6.
The Gulf of Tonkin, including Bach Long Vi, is forecast to see level-5 winds, rising to levels 6-7 with gusts of level 9 near the depression's centre. Waves could reach two to four metres, with rough seas.
Vessels in affected waters could face thunderstorms, strong winds, high waves and possible tornadoes.
From Tuesday evening through Wednesday, northern Vietnam and Thanh Hoa are forecast to receive 15-35 mm of rain, with some areas seeing more than 80 mm.
Thunderstorms could bring tornadoes, lightning, hail and strong gusts, potentially damaging trees, homes, transport infrastructure and other facilities, as well as affecting agricultural production.
Localised heavy rain could also trigger flash floods in small rivers and streams, landslides on steep slopes and flooding in low-lying areas.
