"We are reviewing exactly what has happened in these circumstances because they cannot be repeated," Prime Minister Jacinda Ardern said.
Yesterday compassionate leave for those in quarantine had been suspended.
In a Facebook message last night, Ardern said that would not change unless testing was "rigorous".
There was an expectation that anyone who came into from overseas was in quarantine for two weeks and would not leave without being tested, she said. "That was where there was a failure in this case."