A tropical low pressure system is developing at sea south of Ca Mau and Kien Giang provinces, the National Hydrometeorological Center warned on September 23.
With heavy showers, strong winds and thunderstorms forecast for the next few days, ferries connecting the mainland to the resort island of Phu Quoc in southern Vietnam will be suspended.
Ferries are the main means of transport to the island, carrying about 200 tourists a day.
The suspension is for passengers' safety. Vessels would only resume transport when the weather calms down, the authorities said.
Full refunds will be available for affected passengers.
The tourism season for Phu Quoc is from December to March. The island, home to many luxury resorts and serene beaches, is one of the most popular tourist destinations in the south.
In the first nine months of this year, Phu Quoc has welcomed 2.8 million visitors, well exceeding the target of 1.8 million set at the beginning of this year.