Among the rescued was boat captain Bui Van Toan who said when the incident happened, the boat was returning ashore from a fishing mission around the Truong Sa (Spratly) islands.
Strong winds and high tidal surges of up to 2-2.5m sank the boat at around 17.00pm, Toan said.
Another boat fishing nearby failed to reach Toan’s vessel in distress, and it sent an SOS message to the mainland for help.
The Border Guard Command of Binh Thuan province dispatched rescue ships to the waters where the boat sank, and called for help from other fishing boats nearby.
Bad weather hampered rescue work.
By noon July 9 thirteen fishermen had been rescued, and six others remain missing.