There have been four positive cases of Covid-19 outside of managed isolation or quarantine, Prime Minister Jacinda Ardern says.
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.
She reiterated the message of "going hard and going early".
"In line with our precautionary approach we will be asking Aucklanders to take swift action with us."
Auckland moves to level 3 restrictions from 12 noon tomorrow. The restrictions will last three days until midnight Friday.
"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, 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 their symptoms.
All key services, including pharmacies and supermarkets remain open. Food delivery is available under level 3.
The rest of the country outside of Auckland will move into level 2.
The level 2 restrictions are in place from midday tomorrow until midnight on Friday.
New Zealand is now activating a resurgence plan.
Director General of Health Dr Ashley Bloomfield says there are four confirmed cases within one family.
One person is in their 50s. They live 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.
All close contacts are in isolation.
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."
While there are four positive cases in one household, more than one workplace is involved.