The officer who shot and killed a machete-wielding man in Porirua last year only had the gun because there was a shortage of Tasers at the time.

Officer E, a dog handler with 12 years' experience, had to make a split decision to shoot when 44-year-old Christopher Brown was less than a metre from him with the raised machete.

The Independent Police Conduct Authority released a report today clearing police of wrongdoing over the February 26 shooting.

Brown had violently assaulted his partner and damaged her Waikanae home before driving away from the property armed with the machete and a slug gun.

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Police found and trapped Brown in the Porirua suburb of Mana, surrounding his car with police vehicles so he could not drive away.

But within five seconds of Brown getting out of his car, Officer E had to decide to shoot him or be hit with the machete.

Brown wouldn't respond to the officer's shouted instructions to drop the machete, but raised it and started advancing.

"It was menacing. It was like he was a man on a mission. He was in robot mode," Officer E said.

"It would only take one hit with a machete to either incapacitate me or render me ineffective to fight against him."

Officer E yelled: "Stop, armed . . ." but did not finish the instruction before realising Brown was close enough to hit him with the machete.

He fired once at Brown through a gap between the windscreen of his vehicle and the open driver's door. He told the authority he fired to "protect myself".

The bullet hit Brown's right shoulder.

The authority found officers did all they could to save Brown, but he died on the way to hospital.

Its report revealed the officer wasn't carrying a Taser because there weren't enough in the Wellington district for dog handlers to have one.

But the authority believed even if Officer E had had a Taser, it wouldn't have been enough to stop Brown.

"Mr Brown presented an immediate threat of death or serious injury to Officer E. There was too great a risk that a Taser would have failed to incapacitate Mr Brown for it to be a reasonable tactical option in these circumstances."

Officer E didn't believe pepper spray or a baton would have been enough protection against the machete, and he had no time to run to the police van and get his dog out before Brown reached him.

He also did not want to retreat as he was unaware of the other officer's position and didn't want him to be exposed to the same threat.

"As a police dog handler, Officer E had a high level of tactical training and significant experience in dealing with highly aggressive and dangerous people. He said that he did not know if Officer C had the same tactical skills as he had," the report said.

The other officer had drawn his gun rather than his Taser when coming to Officer E's aid, believing Brown intended to kill both of them, the report noted.

Wellington now has enough Tasers and police policy has changed so dog handlers must have access.

The authority concluded police response was appropriate and the officer's actions in firing his weapon were "lawful and proportionate".

"The death of an individual is not the outcome that anyone wants," Wellington district commander Superintendent Sam Hoyle said.

"No police officer wants to have to use lethal force however police staff must act to keep themselves and communities safe and in this case the officer was faced with a violent individual who was armed and in an agitated state.

"This was a tough and traumatic incident for everyone involved."