A St John spokeswoman said it was notified of the incident in North Taieri Rd outside Abbotsford School about 12.10pm yesterday.
An ambulance and two rapid response vehicles were sent and the boy was taken to Dunedin Hospital in a critical condition, the spokeswoman said.
Senior Sergeant Anthony Bond, of Dunedin, said this morning that the child was run over by the truck's left rear tyres.
The 59-year-old female driver of the small truck was turning the corner left on North Taieri Rd from Abbots Hill Rd when the incident occurred, Snr Sgt Bond said.
He believed the 8-year-old victim was moving along the footpath, looking into North Taieri Rd, not at the intersection or traffic, when he walked into the side of the moving truck, falling to the ground and being run over by the truck's left rear tyres.
An investigation was ongoing, he said.
Four police cars attended the incident.
A small truck carrying metal was seen parked on the left side of the road.
A resident of a nearby house said he had not witnessed the incident, but his mother had run out to the street when it happened.
A big group of people had gathered around a child who was injured, he said.