There have been four positive cases of Covid-19 outside of managed isolation or quarantine, Prime Minister Jacinda Ardern says.
After 102 days without community transmission they are the first cases acquired from an unknown source. New Zealand is now activating a resurgence plan.
Ardern said we must take a "precautionary" approach as no origin had been found, or link to isolation facilities or people who work at the border.
As a result, Auckland moves to level 3 restrictions from 12 noon tomorrow. The restrictions will last three days until midnight Friday. The rest of New Zealand will move to level 2 at the same time.
"These three days will give us time to assess the situation, gather information, make sure we have wide-spread contact tracing," Ardern said.
Aucklanders are asked to stay home to stop the spread. "Act as if you have Covid and the people around you have Covid."
Under level 3 in Auckland, people are to work from home unless they are essential workers, and stay in their bubbles. Bars and restaurants will have to close, and restrictions come in place for funerals and weddings.
"Travelling into Auckland is prohibited unless you normally reside there and are travelling home."
People in Auckland but not from the city can return home, but must be aware of symptoms. Anyone with symptoms is advised to get a test
All key services, including pharmacies and supermarkets remain open. Food delivery is available under level 3. Childcare and schooling is only available for essential workers.
The government would provide the public with an update on Friday.
Ardern said she did not want to "predetermine" what might happen after that.
Director General of Health Dr Ashley Bloomfield said the four confirmed cases were within one family.
The first case was a person is in their 50s who lives in South Auckland. They have returned two positive results. They have no history of international travel.
Six family members who reside in the same household have been tested. Three returned positive results, three negative.
The government is discussing with the family a possible move to a quarantine facility, Ardern said.
All close contacts are in isolation.
While the cases were in just one household, more than one workplace was involved.
Bloomfield said there would be testing of people working at the borders and in facilities to determine the origin of this case.
Testing centres in Auckland will operate with more staff and longer hours in coming days,
DHBs are also planning "pop up clinics", Bloomfield said.
The Ministry of Health would work closely with DHBs throughout the country to ensure there are enough tests to meet demand.
"As we did in the early days of the virus emerging, we need to stamp it out," Bloomfield said.
People need to practice good hygiene, wash their hands, stay at home if sick and stay 2m from others if possible, Bloomfield said.
People are also encouraged to use a mask "in spaces and places where it is hard to physically distance".
Bloomfield said the Covid tracer app would be essential in contact tracing, and urged people to download and use it.
"The case is a wake up call for any complacency that may have set in ... we have done this before and we can and will do it again."