A police staff member is fighting for his life in hospital after the speed camera van he was in was struck from behind by another vehicle.
The driver of the second vehicle was pronounced dead at the scene.
Police and emergency services were called to the crash near the Tauhinu Rd off-ramp, at the Greenhithe Rd overbridge, just after 10am.
"Sadly, police can confirm one person has died at the scene. Another person has been seriously injured and is being taken to hospital."
Police have since confirmed that one of their own was critically injured in the collision, after it was revealed that the van involved was a speed camera vehicle.
Commissioner of Police Andrew Coster said: "The employee was on duty in a speed camera van when the crash happened shortly after 10am today.
"Our staff member was seriously injured and taken to hospital in a critical condition. He is currently in hospital undergoing surgery."
Coster said police have notified the man's family and are supporting them in every way at this time.
"This incident is also incredibly distressing for our wider police family, who go to work every day to keep New Zealanders safe in their communities and on the roads."
The full circumstances of the crash are not yet known and the Serious Crash Unit is investigating.
"Police remain at the scene and the Serious Crash Unit and Waitematā CIB are investigating the cause of the crash."
Authorities are also supporting the family of the driver who was killed. Victim support is also being offered.
St John earlier said four ambulance vehicles were sent to the scene after they received reports of a crash at 10.10am.
Waka Kotahi NZ Transport Agency said the highway is now closed, eastbound, between Tauhinu Rd and Albany Highway.
"[It's] likely to remain closed for some time as police undertake an investigation," NZTA said.
Those travelling for essential purposes in the area are told to allow for extra time, as a detour has been put in place.