Fifteen people have died after a speedboat carrying Indian tourists capsized near a island in the south of Vietnam, according to local media reports.

Local authorities say 32 Indians and four crew were on board the vessel, which overturned about 400 metres (1,312 ft) from Hon May Rut Ngoai island in rough sea conditions on Saturday.

Several tourist vessels operating in the area quickly came to the rescue, finding many passengers trapped inside the speedboat, Vietnam's VnExpress reported. Twenty one people were later saved.

Hon May Rut Ngoai – a pristine island in the An Thoi Archipelago in the Gulf of Thailand – attracts many tourists from around the world for island-hopping boat tours.

Hon May Rut Ngoai is located about 10km (six miles) south of Phu Quoc, Vietnam's largest island.

Nguyen Tien Hai, a senior Communist official in the area, said the authorities were still working to confirm the exact number of those who died as well as the survivors.

He is quoted by VnExpress as saying that the speedboat may have capsized due to heavy winds and high waves.

"The top priority is rescue, bringing all victims ashore and focusing all efforts on providing emergency care to those who are still alive," Hai said.

The Indian embassy in Vietnam described the incident as "tragic", publishing the full list of the 32 Indian nationals who were on board the capsized boat.

The embassy also set up the telephone hotlines to "provide information and assistance to affected families".