Fifteen Indian tourists died on Saturday when a speedboat capsized in rough waters off Phu Quoc island in southern Vietnam, according to local authorities. The vessel, carrying 32 Indian passengers and four crew members, overturned about 400 metres from Hon May Rut Ngoai island while returning from an island-hopping tour to An Thoi port, Vietnamese state media reported.

Rescue operations involving nearby tourist boats, border guards, the navy and coast guard pulled 21 survivors from the sea, though many passengers were trapped inside the overturned hull, eyewitnesses said. Two survivors remained in critical condition at local hospitals, medical sources said. The Indian embassy in Hanoi confirmed the death toll and released a list of the deceased, identifying 10 victims from Tamil Nadu, three from Andhra Pradesh and two from Kerala.

The cause of the accident was not immediately clear. Phu Quoc authorities said preliminary assessments pointed to heavy winds and high waves, while some survivors described the boat overturning within seconds, possibly due to overloading. The speedboat operator, Ocean Pearl Island Company, held all required permits, a local Communist Party official told state media. Vietnamese Prime Minister Le Minh Hung ordered an investigation and a review of maritime safety in the area.

Phu Quoc, Vietnam’s largest island, has seen a surge in tourism, drawing millions of visitors annually to its beaches and coral reefs. The Indian tourists were part of a company-sponsored trip for dealers of a smartphone manufacturer, according to a statement from the firm. The Indian embassy set up emergency helplines and said it was coordinating with Vietnamese authorities to repatriate the bodies. The investigation into the capsizing is ongoing.