Police officers cordon off an area after a shooting incident in Auckland. AFP
Police said the officer and a colleague were carrying out a routine traffic stop involving a car carrying two people when one of them produced a rifle and opened fire.
One officer died, another received serious leg injuries and a member of the public was hospitalised after being struck by the fleeing car, commissioner Andrew Coster said.
Police immediately launched a massive search for the two men.
"This was the type of work that our officers undertake every day to keep the public safe," Coster told reporters.
"At this stage, there is nothing to indicate that this job was going to be anything out of the ordinary."
He declined to speculate on a possible motive for the shooting.
Ardern offered condolences to the officer's family and police colleagues.
"This is devastating news. Our police officers work hard every day to keep us and our communities safe,” she said in a statement.
Armed police flooded the suburb of Massey in west Auckland searching for the offenders but Coster said they had not yet been found.
The officer is the 23rd to be shot dead on duty since 1890, according to the police website, with the previous fatal shooting in 2009.
Coster said the officers involved in the Auckland incident were unarmed.
Police last week decided against introducing armed patrols and Coster said the shooting would not prompt him to revisit the issue.
It comes just a day after parliament voted to further tighten New Zealand's firearms laws in the wake of last year's Christchurch mosques massacre, when a lone gunman murdered 51 Muslim worshippers.
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The bodies of two victims from New Zealand's mosques mass shooting were carried in open caskets on the shoulders of mourners into a large tent at Christchurch's Memorial Park Cemetery on Wednesday - the first burials of the 50 victims.
New Zealand police found a suspected bomb and ammunition on Tuesday in a vacant lot in Christchurch, the scene of last month’s mosque shootings which killed 50 Muslim worshippers.
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