The truck overturned in Thanh Hoa province on Friday evening.
Police in the northern province of Thanh Hoa said a truck may have been overloaded when it flipped over on a national highway, killing three people and seriously injuring four others.
The accident happened at around 8 p.m. on Friday when the truck driven by Nguyen Van Tan with six men on board was going down a hilly section of National Highway 15C through a mountainous village.
Tan reportedly lost control of the truck before it plunged off the road and overturned.
Three men in the truck, aged 23-30, died on the spot.
Four others, including Tan, were severely injured. They are being treated at a local hospital.
Police said the truck may have been overloaded and lost balance when it went down the hilly road, causing the accident. The road was also slippery due to rains and the weather in the area was foggy over the last few days.
Investigations are ongoing.