Emergency services are at the scene of a serious crash on State Highway 8, near the Lake Pukaki Visitor Centre.
Police received a report of a car vs campervan crash at around 2:15pm.
Police say two people suffered serious injuries and two have moderate injuries.
Helicopters have been dispatched, two from Christchurch and one from Dunedin.
An eye witness says traffic is building up and a 4th helicopter has arrived on scene.
He says the campervan is on its side.
The Serious Crash Unit has been advised.
The road is blocked.
Motorists are advised to avoid the area.