“What has happened here is individuals have been granted compassionate leave under circumstances that it is quite clear they should not have been,” she said.
Speaking in a Facebook Live on Tuesday evening, the prime minister said the two new cases “were not announced under the circumstances we would have expected at our border”.
“Those circumstances we do not consider acceptable,” she said.
Ardern said the fact that testing had occurred outside the isolation facility “does not meet our expectations”, and said these circumstances “cannot be repeated”.
“The requirements put around in this case, or the checks and balances in this case, were not adequate – no question.”
On Tuesday, the government confirmed that COVID-19 was active in New Zealand again after two women who had recently travelled from the UK had tested positive for the virus.
The testing took place after the women had been allowed to leave a managed isolation hotel in Auckland to travel to Wellington in a private vehicle on compassionate grounds.
Compassionate exemptions have been suspended while the government reviews processes.
The new cases ended a 24-day streak of no new infections in New Zealand.
The two women were members of the same family who arrived in New Zealand on 7 June, having travelled via Doha and then Brisbane.
Director-general of health Dr Ashley Bloomfield said there was an additional family member who may be at risk who is being tested and isolated.
Other potential contacts with the two women include those who were on the Brisbane to Auckland flight on 7 June and those who were in the same managed isolation facility in Auckland, including staff. The women had been at the Novotel Auckland Ellerslie hotel.