BEIJING — Preparations for China’s traditional Dragon Boat Festival races took a tragic turn on Saturday when 17 people died after two dragon boats flipped over, throwing dozens of paddlers into the churning water.

The accident in the Guangxi region of southern China happened during training for the popular event, also called the Duanwu Festival, which will be held in June and features long boats powered by dozens of paddlers racing along rivers and reservoirs.

When two of these boats tried to pass an overflow dam on the Taohua River, they capsized and 57 people onboard fell into the fast-flowing water, an official Guangxi news website and other outlets reported on Sunday. Video on one Chinese news website showed a boat approaching the overflow barrier sideways and suddenly being sucked under while onlookers shouted in dismay.