Five men died and another was in critical condition after their van plunged about 10 meters into a dam reservoir in Osaka Prefecture, police and firefighters said.
The six employees of an Osaka construction company were on their way home from a barbecue Sunday with 17 others at a camping site around 2 km south of the dam in the city of Kawachinagano, the police said.
Of the five who died, two were in their 60s and three in their 50s.
Immediately after the van entered the water, some of the men were extracted by colleagues who were trailing in other vehicles and rushed to a hospital.
The police said they suspect driver error caused the accident since there aren't any skid marks on the road. Guardrails were found torn down along about 15 meters of road where the van apparently veered off.