Wellington - A heavily-armed man suspected of killing a New Zealand police officer remained holed up in a suburban house as darkness fell on Friday after refusing appeals from police and his family to give himself up for two days.

Police described the man as a "very complex character who has gone through a number of mood swings" during a second day of on-and-off talks in which he telephoned them as well as answering calls from specialist surrender negotiators.

The former reservist soldier, dubbed a "total Rambo" and a "gun nut" by friends, is believed to have a stash of explosives as well as several firearms and plenty of ammunition and police indicated they were prepared to sit out the standoff and await his surrender.

Police superintendent Sam Hoyle told reporters the siege could be over in minutes if the 51-year-old suspect, accused of gunning down three unarmed officers, one fatally, when they confronted him with a search warrant for cannabis on Thursday morning, surrendered.

But Hoyle added, "We are preparing for it to go for some days," and said he could give 170 residents evacuated from the area on a hill overlooking the North Island city of Napier no idea of when they would be able to return to their homes.

As night fell, an army armoured personnel carrier moved up towards the house and after a volley of shots, police announced that they had recovered the body of the dead officer, which had lain in the driveway since he was shot on Thursday morning.

Police flew in reinforcements overnight from all over the country to replace officers who had been on the operation since the drama started Thursday morning when the three officers went to the house on what was supposed to be a routine, "low risk" search for cannabis.

New Zealand police do not routinely carry weapons, and were unaware that the suspect, who did not have a firearms licence, possessed at least two high-powered rifles.

He shot them and an unidentified member of the public, who police revealed Friday had tried to wrest a high-powered rifle from the gunman as he fired.

The three survivors remained hospitalized in critical condition with gunshot wounds.

The mother and brother of the suspect identified him as Jan Molenaar, who friends described as a loner obsessed with physical fitness and guns.

His distraught mother, Anna, apologized to police in a Television New Zealand interview and asked what her son was trying to protect: "A silly marijuana plant? What a thing to protect ... and take someone's life."