Three staff members on a ward used specifically for the care of Covid-19 patients at Auckland's North Shore Hospital tested positive for the virus after Labour Weekend.
A Ministry of Health spokesperson says the source of transmission is being investigated and North Shore Hospital has undertaken a precautionary review of its ward systems.
Testing of staff has revealed no further positive cases.
The ministry says all staff members in Covid-19 wards are double-vaccinated, wear appropriate PPE and undergo health screening at the start of each shift. The first case was identified through staff surveillance testing.
It comes after New Zealand recorded a record-breaking 162 new daily cases on Monday, including 156 in Auckland.
One of the new cases is a second staff member at Edmonton Meadows Care Home in Auckland's Henderson to come down with the virus.
The total number of cases related to the rest home is now 10. Two Covid-positive residents are receiving care at North Shore Hospital.
The source of transmission at the care home remains unknown.
So far, 70 of the new cases are linked to the current Delta outbreak, with the remaining 92 yet to be linked.
There remains 421 unlinked cases from the past 14 days.
The total number of cases in this Delta outbreak is now 3510, of which 1631 have recovered.
There are now 53 people with Covid-19 in hospital, down from 56 on Sunday, including three in intensive care or a high dependency unit.
There are 19 cases each at Auckland City Hospital and Middlemore Hospital, and 15 at North Shore Hospital.
The average age of people with Covid-19 in hospital is 47.