Vietnamese officials have begun to evacuate around 400,000 people as a typhoon with winds of up to 120km/h (75mph) approaches.
Fishing boats are being grounded or anchored in sheltered rivers
Typhoon Lekima is expected to hit Vietnam's central provinces on Wednesday night and then move inland to the north-west.
Vietnam's national weather forecast centre has warned local authorities of possible flash floods and landslides.
Central Vietnam is in "extreme danger", the government said.
Lekima, named after a Vietnamese fruit, was upgraded from a tropical storm to a typhoon on Wednesday afternoon, according to the Associated Press.
Lekima made landfall late on Tuesday near China's beach resort of Sanya on the southern tip of Hainan Island, where more than 225,000 residents were reportedly evacuated.
In Vietnam, an area stretching more than 300km (190 miles) between the central provinces of Thanh Hoa and Quang Binh faced "extreme danger" and would need to be evacuated, the government said.