According to the National Centre for Hydro-Meteorological Forecasting, Storm No. 4, internationally known as Narra, remained over waters off Quang Ninh and Haiphong on Saturday morning.
At 10 am, the storm's centre was about 120 kilometres north of Bach Long Vi Special Zone, with maximum sustained winds of 62-74 kilometres per hour and gusts of up to level 10 on Vietnam's wind scale. It was moving southwest at around five kilometres per hour.
Strong winds were recorded across coastal areas, including Bach Long Vi, Co To and Mong Cai, while Uong Bi and Haiphong's Phu Lien station also reported strong winds.
The storm is forecast to move slowly southwards by Sunday before turning east-southeast on Monday and northeast on Tuesday at three to five kilometres per hour. It is expected to maintain its intensity before gradually weakening into a tropical depression.
Across the Gulf of Tonkin and coastal waters off Quang Ninh and Haiphong, winds are forecast at force 6-7, rising to force 8 with gusts of force 10 near the storm's centre. Waves could reach two to four metres.
Forecasters warned that rough seas could damage or sink fishing, cargo and tourist vessels, while aquaculture facilities, anchorages and coastal infrastructure could also be affected.
Coastal areas of Quang Ninh and Haiphong could see winds of force 6-7 and gusts of force 8-9, posing risks to roofs, temporary structures, trees, billboards, power supplies and transport.
Rainfall could exceed 600 mm
From August 22 through the night of August 24, the northeast, southern Phu Tho and Thanh Hoa are forecast to receive 100-200 mm of rain, with some areas exceeding 400 mm.
Quang Ninh and Haiphong are expected to receive 250-350 mm, with isolated totals above 600 mm, while Lang Son and Bac Ninh could see 200-300 mm and locally more than 500 mm.
The heavy rain could persist beyond August 24, raising the risk of urban and industrial flooding, as well as flash floods and landslides in mountainous areas.
The General Staff of the Vietnam People's Army on Saturday issued an urgent directive ordering military units to prepare personnel and equipment for disaster response and help deal with flooding caused by the storm.
Military regions were instructed to identify areas at high risk of flash floods, landslides and inundation, as well as vulnerable dykes, reservoirs and dams.
Troops were also told to help residents secure homes and farms and evacuate people from areas at risk of landslides, flash floods and deep flooding.
Border guards from Quang Ninh to Thanh Hoa were instructed to track vessels at sea, update crews on the storm and guide them away from dangerous waters to safe shelters.