"We're moving now because the advice we have is that we do not have widespread, undetected transmission in Auckland," she told reporters.
"If everyone continues to play their part, we can continue stamping out (the virus)."
The change means stay-at-home orders will remain in place but some businesses, such as takeaway food outlets, can open using contactless delivery.
New Zealand imposed a nationwide lockdown on August 17 when the first case of the highly transmissible Delta variant was found in the community.
The cluster has been concentrated in Auckland and the rest of the country moved out of lockdown earlier this month.
Ardern said the North Island city could do the same when authorities were confident the outbreak was "well contained".
"At the moment, we continue to see mystery cases cropping up through community testing," she said.
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"We want to see a turnaround in some of these situations."
New Zealand is pursuing a "Covid zero" elimination strategy -- which has resulted in just 27 deaths in a population of five million.
The country had been free of community cases for six months before the August outbreak, with residents enjoying a near-normal domestic life alongside tight restrictions on international borders. /AFP