An inmate in Mt Eden Prison has been confirmed as one of Sunday's new community cases of COVID-19.
The man was taken into custody on Friday night and his infection is yet to be linked to the original Delta outbreak.
"Whilst we've not formally linked the case yet, there is a tentitive link but more is being done to sure that up - but I want to acknowledge both the police staff and the Corrections staff involved in this case," Prime Minister Jacinda Ardern told reporters.
Director of Public Health Caroline McElnay confirmed four police staff were in isolation as a result. Five Corrections staff have also been identified as contacts and are isolating, she said.
"He is understood to have been in the Firth of Thames area before he was taken into custody - this is within the Counties Manukau DHB area and is under alert level 4 restrictions," Dr McElnay said during Sunday's COVID-19 update. "He was travelling with one other person who's now in isolation and is being tested today."
The case and his contacts have been cooperative with health authorities, said Dr McElnay.
Speaking after Dr McElnay, Ardern acknowledged the "extraordinarily rigorous" Corrections protocols that led to detecting the Mt Eden case.
"Corrections treat, in level 3 and 4, new incoming prisoners as they would an individual coming in at our border," Ardern said.
She said prisoners are tested for COVID-19 on arrival and have regular tests until day 12.
"They work through a process to ensure that someone is COVID-free before they're integrated more fully into the prison environment.
"Off the back of that testing they've detected this new case."