A witness said there were injured people "everywhere". Emergency services personnel were working frantically to rescue "screaming" people from "mangled" vehicles.
A northbound Mitsubishi people-mover with six occupants collided with a small, southbound Toyota car containing three people at the intersection of State Highway 1 and Maheno-Kakanui Rd near the Kakanui River bridge about 6pm.
Sergeant Blair Corlet, of Oamaru, said two people trapped in the Mitsubishi were in a critical condition; they were freed by firefighters using the jaws of life.
Three other occupants received serious injuries, and a fourth had moderate injuries.
The 42-year-old Waimate woman driving the Toyota was seriously injured and her passengers - a 1-year-old baby and a 16-year-old - received moderate injuries.
All were taken to Dunedin Hospital in the three rescue helicopters and three ambulances sent to the scene.
The highway was closed in both directions after the crash, and detours were put in place until the highway reopened about 7.30pm.
Sgt Corlet said a Serious Crash Unit from Invercargill was investigating the crash. Police were still at the scene late last night.
7 hurt in crashes around country
Seven people were injured in three other road crashes in New Zealand at the weekend.
A Mercedes crashed into a tree at Horotiu in the Waikato at 10.45am yesterday, leaving the driver with critical injuries.
The front-seat passenger had moderate injuries.
Three people were injured, one seriously, after a tour bus and rental car collided near Christchurch International Airport, at the intersection of Wairakei Rd and Orchard Rd, at 9.15am on Saturday.
One person had serious injuries and two others were left with moderate injuries, a police spokeswoman said.
Two people were injured when a car plunged off a bank on State Highway 25 in the Coromandel just after 9am on Saturday.
