Fifty-five prisoners and 21 staff at Auckland Region Women's Corrections Facility are isolating after a positive Covid-19 case.
A staff member tested positive yesterday morning following self-isolation and testing after a household member tested positive.
The staff member last worked at the prison between 17 and 20 December.
Regional Commissioner Lynettte Cave said staff were stood down and the 55 prisoners were in separate units isolating.
All prisoners have been tested. Staff were asked to isolate and get tested.
In a statement, Cave said the prison took immediate action when alerted to the fact a staff member was close contact of a positive case and began contact tracing as a precaution.
The prison is at Covid-19 Protection Stage 2.
"This means no face-to-face visits for private and legal visitors took place during the period the staff member was on site," Cave said.
"We appreciate that this may be distressing for women accommodated within the prison and staff have been reassuring them frequently and distributing information sheets so that they know what has happened, and what they need to do to prevent Covid-19 from spreading.
"I would like to assure the whānau and friends of women at the prison that all of the women are safe and well, and the Christmas meal and activities planned for today are continuing - with additional physical distancing and PPE use."
Welfare support was in place for staff and inmates would be cared for by Corrections health and custodial staff, Cave said.
Latest figures show 67 percent of women in prison are fully vaccinated.