A staff member at Auckland City Hospital has tested positive for COVID-19.
It's one of four new cases, a spokesperson for COVID-19 Response Minister Chris Hipkins told Newshub.
The hospital staff member was a nurse who was fully vaccinated.
All the cases are linked to the 58-year-old man who tested positive for the Delta variant of the virus on Tuesday.
"We have a staff member who has tested positive for COVID-19," the email to Auckland District Health Board staff, forwarded to Newshub, reads.
"We are concerned about a hospital outbreak and we are therefore taking a number of precautions. We will be carrying out a detailed contact trace over the next day but in the meantime if you have been in Ward 65 in the last five days please contact Occupational Health and get a COVID test."
Staff were told to wear a mask "at all times", be "really careful about hand hygiene", "restrict your movement around the hospital", and work from home if possible.
"This situation is likely to evolve over the next few days," the email said. "We will provide frequent updates so you can understand what’s happening and what it means for you."
Updates were promised on Wednesday.
New Zealand is currently at alert level 4 to prevent further spread.