A speedboat carrying Indian tourists capsized off Vietnam's southern island of Phu Quoc on Saturday, killing at least 15 people, state media reported.
The vessel, carrying 36 people, overturned about 400 meters (440 yards) off May Rut Ngoai Islet, according to the VnExpress news website.
Tourist boats and coast guard vessels joined a rescue operation, pulling several survivors from the water.
The Tuoi Tre newspaper, citing local police, reported that 21 people were taken to a hospital for emergency treatment, two of them in critical condition.
All 15 of those killed were foreigners, according to Tuoi Tre.
India's Embassy in Vietnam confirmed that the capsized boat had been carrying "several Indian tourists" but said "exact details of the incident are being ascertained."
Nguyen Tien Hai, a provincial official with the ruling Communist Party, said authorities were still confirming the exact number of survivors, according to state media.
Hai said initial assessments suggested the speedboat overturned because of strong winds and high waves.
Located just south of Phu Quoc, Vietnam's largest island, May Rut Ngoai is known for its clear blue waters, white-sand beaches and diving reefs.
Visitors typically reach the islet by speedboat from Phu Quoc.
Phu Quoc has experienced a tourism boom in recent years, with more than 1.8 million foreign visitors arriving on the island last year.
Boating accidents are common in Vietnam, where extreme weather, persistent flooding and poor maintenance have contributed to frequent tragedies.
In July last year, 39 people were killed when a tourist boat carrying families around northern Vietnam's famed Ha Long Bay capsized after being struck by a sudden storm.
