Police say a 12-hour motorway closure after a fatal shooting north of Auckland was "regrettable" but they make no apologies to frustrated motorists for doing their job.

A 27km stretch of State Highway 1 near Puhoi was closed to all traffic on Saturday after a man was shot dead by police.

He was killed after confronting officers with a machete just before 4am and the road was closed immediately.

It did not reopen until 3.55pm.

The closure created traffic chaos for hundreds of people heading out of the city for the long Easter weekend.

Police have been heavily criticised by members of the public for the closure - primarily for the length of time they had the area shut down to traffic.

Today, Inspector Trevor Beggs, road policing manager for the Waitemata District, explained exactly what was happening inside the cordon and why it took 12 hours to clear the scene.

"That location is often associated with serious crashes, and in that situation the Serious Crash Unit will get in, do what they need to do and be out in a couple of hours," he said.

"But this was a firearms incident, a much more complex and difficult scene.

"We only get one chance to gather evidence and to do the best job we can."

Police are investigating the death of the 29-year-old alongside parallel investigations by the Coroner and Independent Police Conduct Authority.

Beggs said it was crucial to ensure every piece of available evidence was collected - including physical evidence, scene photographs and mapping of the area.

"We had a range of people who came in to the scene, including outside agencies," he explained.

"There were the initial staff who responded, then detective teams, then the photography section, mapping, ESR forensic staff and others.

"The ESR guys are often in their on their hands and knees looking for vital evidence."

Beggs said there was no way the scene examination could have been completed any faster.

He visited the scene himself and saw staff "under pressure" to get the job done - and properly.

He received half-hourly updates and worked with transport agencies to update them on the status of the road closure.

"We wanted to do the best job for everyone concerned," he said.

"The family of the deceased of course, the police staff involved and everyone else.

"We really needed to be in there gathering all the evidence we could."

Beggs said the location of the incident made traffic diversion challenging.

"If this had happened a few kilometres back down the road at Albany, we could have diverted people off the motorway there (along the alternative toll-free route)," he said.

"But because of where the scene was, we didn't have many options available to us.

"Unfortunately it was one of the busiest, if not the busiest weekend of the year and there was a high demand on the road - it was the worst possible time for an event like this to happen."

Beggs thanked motorists for their patience and hoped those criticising police for the delays would understand how and why it had happened.

"This happened at 4am and we had to wait until daylight for most of the work at the scene to begin," he explained.

"The geography made it more difficult, and it was a complex case with multiple investigations.

"It was regrettable that it took so long, but unfortunately that could not be helped.

"I visited the scene and I was comfortable that staff were working flat out to get that road opened - literally, people were doing their absolute best to get everything done.

"At the end of the day, we had one chance to get it right - and we needed to get it right."

The investigations into the death of the 29-year-old from East Auckland are ongoing.

His name will not be released until after his funeral, at the direct request of his family.

Police are appealing for anyone who saw the victim's car to contact them.

"We are specifically interested in any sightings of the vehicle in the Rodney area between Silverdale and Warkworth on State Highway 1 between 1.20am and 4am on Saturday 31 March 2018," Detective Inspector John Sutton said yesterday.

Man down - how the police shooting unfolded

Police were initially called to an address in Onehunga by a woman reporting that a person known to her had been acting erratically.

She left the scene because she feared for her safety.

Police were sent to the property about 3.10am, however no people or vehicles were there when they arrived.

About 20 minutes later, a rural police officer heading home from a shift saw a car pulled over with its hazard lights on SH1 north of Auckland.

However, the car quickly drove off. The police car followed and the car then stopped again.

As the officer was about to get out of his vehicle the driver of the car got out and came around to the driver's door of the police car, wielding a machete and threatening the officer.

The officer quickly moved away and called for backup. The officer watched the offender from a safe distance.

The alleged offender then got back into his car and headed south on SH1 towards Puhoi.

Additional police resources, including the Eagle helicopter, were called on to help.

The driver was believed to have been travelling at speeds of up to 150km/h and at times with lights off.

Police placed spikes on the road, which successfully stopped the vehicle near Mahurangi West Rd about 3.50am.

As the first officers got out of the police car, the man, still armed with a machete, approached police again.

Police fired shots as he came towards them.

Officers immediately started first aid and called an ambulance, but the man died at the scene.

Can you help?

If you have any information which you think may assist the investigation team, even if it is only minor, please contact North Shore criminal investigation branch on 09 477 5261.