Mr Burke declined to comment on details about the fight, the connection between the men, the man's injuries or the likely cause of his death.
"That's what the post-mortem will establish," he said.
The post-mortem examination, held in Auckland yesterday, would determine if the man died as a result of injuries sustained during the assault. Police would likely be able to release more information about the circumstances today, Mr Burke said. Police and St John spent an hour trying to resuscitate the victim, Mr Burke said.
When a St John ambulance responded to the incident the man was reported as being in a critical condition.
One Newton Rd resident said the road was cordoned off yesterday when she tried to go home. She was unsure who was involved but said it was "very sad".
Another resident who lived further down the street said the first she knew of the death was when she saw a lot of police near the entrance of the street yesterday morning.
A police tent was set up on the verge near two houses, she said. The intense police presence made it "look like a murder scene. For me it's a complete surprise."
About 15 police officers plus the environmental research team were carrying out a scene examination, expected to take all of yesterday, Mr Burke said.
The 39-year-old man was due to appear in Whangarei District Court yesterday.