With a tail of cases still being identified by health authorities, including one new case on Monday, Ms Ardern's cabinet made a majority decision not to relax its current restrictions this week.
Cabinet has agreed to check in on the country's settings at its next meeting, on Monday 21 September.
It made an in-principle decision to move everywhere except Auckland to level one - meaning no restrictions, except for border controls - on that date unless there is an upswing in cases.
The party of Deputy Prime Minister Winston Peters, and Labour's coalition partner, New Zealand First, invoked "agree to disagree" provisions, saying the rest of the country should move now.
"Travelling around the South Island has reinforced that people are not observing social distancing in the absence of any registered or real threat of COVID-19 ... they have applied their own 'common sense' test," he said.
Mr Peters also said the restrictions were costly, "running in excess of $200 million for every week the rest of the country remains in alert level two, as opposed to alert level one".
Ms Ardern, in Dunedin, said "as we know more cases will emerge from this clusters's tail. These cases can continue to pose risks".
"Since the start we have been cautious. This has both saved lives but also meant our economy has been able to remain open in a sustained way. It is a formula that works," she said.
"It only requires one person travelling and attending a super-spreader event somewhere else in the country and we could be looking at further restrictions elsewhere.
"We now need to keep our eyes on that prize and take actions to match that so we can get to level one again. And we will."
The Labour leader said cabinet's decision was consistent with its previous safety-first decision making.
"Last time cabinet made a decision to move down from level two to level one we had spent 26 days at level two ... and had gone 17 days without any new cases of COVID-19," she said.
Monday's sole new case was of a young girl who has a family member to already test positive to COVID-19.
There are currently 96 active cases in New Zealand.
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