One person has died in a serious car crash on State Highway 3 in Waikato and a St John ambulance driver involved in a head-on collision just 30km away has also died.

In the early hours of yesterday morning, a silver Audi and a St John ambulance crashed on State Highway 1 near Cambridge.

The driver and single occupant of the Audi also died.

Around 12.30pm yesterday, SH3 between Te Awamutu and Otorohanga was also closed following a serious crash.

A police spokesperson said one person sadly died in the crash.

The earlier Cambridge crash left debris strewn across SH1 when a car and an ambulance collided. The fronts of both vehicles were completely smashed in by the impact of the crash.

The driver of the car died at the scene, while the driver of the ambulance initially suffered critical injuries and later passed away in Waikato Hospital.

A nurse was also in the ambulance and was injured in yesterday morning's crash near Cambridge, but their injuries are not life-threatening, police said. They too were 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.

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

The detour has affected students sitting exams at St Peter's School.

Earlier, the school told students not to panic and they could sit their exams in the afternoon instead.

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.

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 left onto Maungatautari Rd, straight through to Browning St, right onto Shakespeare St, left onto Achilles St, right onto Albert St, left onto Queen St, then right onto Victoria St before rejoining SH1.

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

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

12 trucks travelling south are queued up at the Karapiro Rd cordon waiting for the road to be reopened. Photo / Caitlan Johnston

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.