A truck driver and his two sons were lucky to escape after their stock truck rolled down a 10m cliff near Norsewood yesterday afternoon.
The driver and boys, both believed to be about 11 years old, were driving north when the sheep truck lost control after hitting a bank. It then crossed the centre line before rolling down the cliff and next to a creek.
It's understood about half of the 500 sheep died in the accident.
Dannevirke police said it was unclear what had caused the truck and trailer, laden with sheep, to go out of control.
Police said they would investigate the circumstances of the single vehicle crash to determine its cause. Road conditions did not appear to be a factor as there was no rain and the road was dry.
A small section of the road was closed and motorists were advised to take an alternative route.
Volunteer fire crews and police were left to round up the balance of the 500 sheep the truck was transporting as they scattered across the road and surrounding countryside.
All three occupants of the truck escaped serious injuries but were taken to Palmerston North Hospital by ambulance for further treatment.
A crane arrived on the scene to remove the truck and trailer wreckage from the side of the road.