Six 6th graders of the Trang Viet Secondary High School in Hanoi's Me Linh District drowned Friday when their boat capsized in the Hong (Red) River.
The accident happened at around noon when the students attempted to pick flowers from a water plant at a river section around three meters deep, after a party held to celebrate the Vietnam National Day.
Le Viet Quen, a local living nearby who managed to rescue one of the students, said he heard them shouting for help.
"The section is rather deep and I could only save one," VnExpress quoted him as saying.
The 6th graders were among a group of 11 students who'd gathered at the riverside after their party ended. Seven of them got into a small boat while four others stayed ashore.
The bodies of six students, all aged 12, were recovered later on Friday.
Nguyen Manh Xuyen, deputy chairman of Me Linh District's Trang Viet Commune, said they would co-operate with district police to investigate the case.
There have been several cases of children drowning in Hanoi this summer. In a recent case, one of three children who fell into the Van Lake drowned, while the other two were rescued.