The bodies of the four men were found in the cabin of the vessel, which was registered in the nearby Ninh Thuan Province.
10 fishermen were on board the vessel, which had started out to fish near the Hon Cau Island on Tuesday afternoon, until waves sank it about one nautical mile away from the island Tuesday night.
Five men were rescued by a Vietnamese fishing vessel. A diving team was later dispatched to approach the sunken vessel and found the bodies on Wednesday morning. One 50-year-old man was still missing. Dozens of fishing vessels have been dispatched to help with searching for him.
The seas of Binh Thuan have been experiencing big waves due to the impacts of the tropical storm Mun, formerly a tropical depression, since Monday. A vessel carrying 50,000 liters of oil were sunk in the province on Monday afternoon and local authorities are preparing to deal with possible oil spills.
Mun is expected to make landfall in the north Thursday morning with winds of 75 kph.
Authorities from numerous provinces and localities, including Quang Ninh which is home to Ha Long Bay, have banned boats and ships from sailing out to sea and advised them to seek shelter from the storm.