The accident left 15 people dead and several were injured as the passengers clung desperately to the overturned vessel.
Seeing them struggle in the rough waters, captain Ha Van Loc steered his tour boat toward the disaster.
"They were being dragged under by the waves but kept waving for help," Loc, 44, an employee of local tour company Dang Khoa Trip, says.
He says at around 12:40 p.m. that day, while sailing from May Rut Ngoai Islet to pick up passengers at Thom Islet, he spotted the overturned vessel in the distance. Both are islets off Phu Quoc Island.
Of around 10 men clinging to the hull and several buffeted in the waters, many lacked life jackets.
