The National Centre for Hydro-Meteorological Forecasting said at 10 am on Friday that the storm had intensified from Category 8 earlier in the morning to Category 8-9, with maximum sustained winds of 62-88 kph (39-55 mph) and gusts of up to 117 kph (73 mph).
The storm's centre was located at 17.5 degrees north and 110 degrees east, about 90 km south of China's Hainan Island, moving west-northwest at around 5 kph (3 mph).
Forecasters said the storm was expected to enter the northern Gulf of Tonkin by 10 am on Saturday, maintaining its strength while accelerating to 10-15 kph.
By Sunday morning, it is forecast to move into southern Guangxi in China with sustained winds of 62-74 kph (39-46 mph) before weakening into a tropical depression on Monday.
A Level 3 natural disaster warning remains in effect for the western part of the northern East Sea, including the Hoang Sa (Paracel) Islands, the northeastern waters from Quang Tri to Quang Ngai, and the Gulf of Tonkin.
From Friday night, strong winds of Category 6-7 are forecast across affected waters, increasing to Category 8-9 near the storm's centre, with gusts of up to Category 11 and waves of 2-4 metres, posing risks to vessels, aquaculture facilities and coastal infrastructure.
Coastal areas of Quang Ninh, Haiphong and Hung Yen are expected to experience strong winds from Saturday afternoon, while storm surges of 0.2-0.4 metres and waves of up to 3 metres could trigger localised flooding in low-lying coastal areas.
Heavy rain is forecast across northeastern Vietnam and Thanh Hoa from Friday night to Sunday, with rainfall of 100-200 mm widely expected and isolated areas receiving more than 350 mm.
Authorities warned that the storm could disrupt fishing, shipping and tourism activities, while heavy rain may trigger urban flooding, flash floods and landslides in mountainous areas.
