A person died and two St John staff were injured in a head-on crash between a car and an ambulance on State Highway 1 near Cambridge, Waikato this morning.

Debris from the crash is strewn across the road and the front of both vehicles were completely smashed in by the impact of the crash. The bumper of the ambulance has landed about 100m away.

The driver of the car died at the scene, while the driver of the ambulance suffered critical injuries and was taken to Waikato Hospital by helicopter.

Another ambulance officer who was in the ambulance was also injured, but their injuries are not life-threatening, Police said. They too have been taken to Waikato Hospital.

"St John was alerted at 3.45am to a fatal motor vehicle incident involving one of our vehicles in Cambridge, Waikato, where tragically the driver of the other vehicle lost their life at the scene," Dan Ohs, deputy chief executive ambulance operations said.

The crash between a car and an ambulance on State Highway 1 near Cambridge killed the Audi driver and two St John staff were injured. Photo / Caitlan Johnston

"Our focus right now is to support our people and our thoughts are with them, their wider family, and friends at this difficult time.

"We are also supporting Police with their ongoing investigations into the crash."

No patients were in the ambulance at the time.

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Police said the road is expected to be closed "for some time" and motorists will need to follow a detour.

The NZ Transport Agency Waka Kotahi said the highway is closed between Karapiro and Cambridge and motorists are being told to follow directions of emergency services at the scene and to allow extra time.

An update just before 7.30am said SH1 remains closed between Cambridge and Karapiro.

Traffic in and around Cambridge is being diverted this morning after a fatal crash in the early hours of today. Photo / Caitlan Johnston

People heading north are told to turn right onto Hydro Rd to Ariki St, right onto Maungatautari Rd, straight through Browning St, right onto Shakespeare St, left onto Achilles St, right onto Albert St, left onto Queen St, then right onto Victoria St before re-entering SH1.

Southbound traffic is advised to use the same route in reverse.

The main road out of Cambridge heading south is closed to traffic.

The road is also closed at the intersection roundabout of Shakespeare and the Explorer Highway. Traffic is being diverted accordingly.

About 10km of the highway is closed and by 8am, traffic was a standstill from the intersection of French Pass Rd and Lovells Rd.

French Pass is a back road from Cambridge that connects through to Karapiro Rd. The distance between the two roads is 13km.

Traffic was free-flowing fairly quickly after the initial congestion.