Two people have been killed after a crash involving a petrol tanker near Marsden Pt in Northland.

And an unmarked police car heading to the smash has also collided with another vehicle, injuring two police officers and the driver of the other car. The crash blocked State Highway 1 about 500m north of the Mangapai intersection.

Police were still at the scene at 2pm and said the road would be closed for some time.

Senior Sergeant Dan Cleaver said the crashed police car was extensively damaged and the two officers were taken to hospital in an ambulance as a precaution.

The only person in the other vehicle was also taken to hospital.

Northbound traffic is being diverted through Mangapai Rd and southbound vehicles are using Maungakaramea Rd, although neither road is not suitable for heavy vehicles.

The road was expected to re-open soon.