An Auckland rest home worker with Covid-19 is a contact of an Omicron case the Ministry of Health says.
Genome sequencing is taking place and the Summerset by the Park Retirement Village in Flat Bush has been placed in lockdown.
It is now closed to visitors and testing is being carried out on residents and staff.
"Anyone who has visited the rest home since Friday 21 January and has symptoms of Covid-19 is asked to isolate and get a test as soon as possible," the ministry says.
The retirement village sent a statement to 1News.
"Late yesterday we were advised a staff member, whose work has been contained to the kitchen, has tested positive for Covid-19.
"Public Health from Counties Manukau District Health Board have advised the village and care centre should be closed for a short period of time until further surveillance testing is completed.
"Staff who have worked directly with the infected staff member are isolating and being tested. All our staff are fully vaccinated.
"As part of our precautionary response procedures, all residents have been asked to stay in their homes or rooms until we have done further Covid-19 testing, a public health testing team is on site today conducting tests.
"Visitors to village residents and care residents are also paused unless there is an urgent need on compassionate grounds."
It comes after Prime Minister Jacinda Ardern announced in a snap media conference that the entire country would be moving to the Red traffic light setting from 11.59pm on Sunday.
Earlier, nine Covid-19 cases in the Nelson-Tasman region were linked to the Omicron variant with no clear link between the affected family and the border, Ardern said.
The cases - all part of the same household - flew to Auckland for a wedding and other events on January 13 before testing positive.
The positive cases led to two further cases, including a flight attendant on the same flight and an attendee at the wedding.