A woman's death after a crash involving a police car is "every police officer's worst nightmare", says Counties Manukau's top cop.
A 4WD the woman was a passenger in and police car collided on Ormiston Road in East Tamaki about 8.30am on Wednesday.
The police car was heading to a "priority one" job with its lights and sirens activated, police said.
The woman, who was aged in her 40s, and the 4WD's male driver both suffered serious injuries in the crash, and the woman died in an ambulance on the way to hospital.
The man remains in a serious condition in Middlemore Hospital.
The police sergeant suffered only minor injuries and was taken to hospital but was later released.
At a press conference at Police National Headquarters in Wellington on Wednesday, Counties Manukau District commander Superintendent John Tims said the police's thoughts were with the woman's family, and with the injured man and his family.
He said the district police would do all they could to support the man, and the sergeant involved.
The woman's name was likely to be released later on Wednesday.
Supt Tims would not comment on how the cars collided, reports the 4WD was reversing out of a driveway at the time of the crash, or what speed the police car was travelling at.
Supt Tims promised an experienced police officer from outside the district would investigate the crash.
"Police are committed to finding out what occurred this morning, not only for ourselves, but for the family," he said.
"We never want something like this to happen."
Fatal crashes involving police cars were "very, very rare", Supt Tims said.
He told media the sergeant involved had been heading to a callout where offenders had broken into a premises, but was unable to give further details about the incident.
One of the alleged offenders had been taken into custody.
The police officer was "distressed and shocked" and would take some time off work to recover, he said.
The serious crash unit was also investigating, while the Independent Police Conduct Authority and coroner had been notified.