The accident happened on State Highway 1, near the Henley-Berwick Rd intersection, about 11.30pm.
It appeared two cars collided. One ended up down a bank beside the road, and a following petrol tanker clipped one of the cars, a police and fire service spokesmen said.
One person with serious injuries, and three others with moderate injuries, were taken to Dunedin Hospital by ambulance, St John said.
The tanker had only minor damage, police said.
The crash came amid a horror start to the school holidays.
Six people were killed in road crashes around the country in the first 24 hours.
The dead included a person killed in a crash on Saturday morning on State Highway 1, south of Waiouru, in the central North Island, and a motorcyclist who died early on Saturday while trying to outrun police in Auckland.
Another person died in Northland on Saturday night after a car plunged into a flooded creek at Omanaia, west of Kaikohe, just before 10pm, trapping a man in the water.
A fourth person died after the car he was driving hit a power pole in Hawera, Taranaki about 4.15pm on Saturday.
A fifth man died after the vehicle he was travelling in left the road and hit a tree on State Highway 1 in Northland early yesterday.
A sixth person died after a two-vehicle crash near Warkworth, which closed State Highway 1 in both directions.
The person was trapped for 40 minutes in a vehicle after the incident, 5km south of Warkworth, yesterday afternoon.
Another person was seriously injured and two others were moderately injured. — Additional reporting The New Zealand Herald
