Students from Dong Hoi High School who were travelling to visit the area in central Quang Binh province for the 30th anniversary of their graduation, were involved in a fatal accident that claimed about 13 lives and many injured on Sunday.
But the driver lost control on a sharp turn on the highway, said state media.
“People on the coach said that when the coach was travelling down the slope, there were signs the brakes were broken,” reported Tuoi Tre newspaper.
Travelling on Vietnam’s roads can be a hazardous affair, and World Health Organization says traffic accident injuries are the leading cause of death for those aged 15-29.
Vietnam has been said to have recorded more than 3,200 deaths in the first six months of this year.