New Zealand's largest city will enter a Level Three lockdown from Sunday at 6am - meaning the city's 1.7million residents must stay at home except for essential shopping and work.
Schools and non-essential shops will close, and entry in and out of the city will be restricted.
The remainder of the country will be under level two restrictions which include limits on the size of public gatherings.
Auckland's new restrictions are in response to a new locally-transmitted case Ms Ardern said could not be directly connected to other positive tests over the last two weeks, although a school in South Auckland was a common link.
The infected man, 20, went to the GP for a Covid test on Friday afternoon but then went to the gym - which Ms Ardern said was 'frustrating'.
Prime Minister of New Zealand Jacinda Ardern (pictured) has announced Auckland will go into lockdown for one week, after just one new local case of Covid-19
'People who should have been in isolation, weren't,' she said of the country's recent outbreak in February.
'Unfortunately, we have still had breaches of requirements in this case.'
Auckland's latest cluster is centred around Papatoetoe High School, and the new case is the older brother of a student at that school.
The mother of the siblings has also tested positive for Covid-19.
However, Ms Ardern said that student has tested negative for coronavirus multiple times.
'That means we have no current known link for the case discovered this afternoon,' she told the media on Saturday afternoon.
'If we cannot immediately link a case person to person, what we call it an epidemiological link, that is a significant issue, and one we need to act on.'
The rest of the country will face tightened public gathering rules under Level Two restrictions.
The rest of New Zealand will face Level two restrictions from Sunday at 6am. Pictured: Testing station in Auckland on February 15
The restrictions are in response to a new community case Ms Ardern (pictured) said does not appear to be connected to a cluster of cases in the south of Auckland
In mid-February, the city was plunged into a three-day lockdown after three members of the same family tested positive for the highly infectious UK strain of Covid-19.
Level three restrictions mean people are confined to their household bubble or an exclusive extended bubble - which may include close relatives or isolated people.
People must work from home if possible and businesses must not offer services requiring close personal contact, unless it is an essential service or emergency.
Public venues are closed but low-risk recreation activities are allowed within bubbles, such as bike riding, swimming or going on a picnic with other household members.
The cluster is centred around Papatoetoe High School, and the new case, a 21-year-old male, is reportedly the older brother of a student at that school. Pictured: A Covid-19 station set up outside the high school on February 15
Level three restrictions mean people are confined to their household bubble or an exclusive extended bubble - which may include close relatives or isolated people. Pictured: Empty Auckland streets during lockdown in August, 2020
These venues have been visited by the new positive case in AucklandPak 'N' Save Manuka: 21 February, 5.30pm-6.40pm Your Health Pharmacy, Papatoetoe: 23 February, 2.45pm-3.50pm Burger King, Highland Park: 25 February, 8pm-9pm Hunter Plaza, Papatoetoe: 26 February, 2.55pm-5pmCityFitness, Papatoetoe: 26 February, 3.20pm-4.40pm and 20 February, 12.20pm-1.45pm. This venue has now closed.
For the rest of New Zealand under Level two restrictions, people can socialise in groups of up to 100, shop and travel domestically.
Schools will remain open and groups over 100 are allowed in cinemas, casinos and stadiums as long as groups of 100 and less do not mix with each other.
Ms Ardern said she was disappointed in those who have not followed the rules and put the community at risk.
'We do have the ability to take enforcement action if we need to,' she said adding that people needed to feel comfortable coming forward.
'We still need an environment where people will speak up and come forward and be tested.'
The newest case is the older brother of a student at Papatoetoe High School (pictured), where the south Auckland cluster originated
The latest restrictions come after the city of 2million people entered a three day lockdown on February 15 when three people from one family - a Papatoetoe High School student and her parents - tested positive for Covid-19.
The city was thrown into a level three lockdown while the rest of the country was placed under level two restrictions.
The mother worked at LSG Sky Chefs, an airport laundry and catering facility at Auckland airport, while the daughter was a student at Papatoetoe High School.
New Zealand has been widely praised for its handling of the pandemic, with just 26 deaths in a population of five million.
NEW AUCKLAND LOCKDOWN HITS SPORTS INCLUDING T20 SERIES
A community coronavirus outbreak in Auckland has forced New Zealand cricket bosses to hastily reschedule two Twenty20 matches against Australia as other affected sports assessed their options.
A New Zealand Cricket spokesman said the third match in the current T20 series, to be played in Wellington on Wednesday, will go ahead but without spectators.
Game four, scheduled for Auckland on Friday, has been moved to Wellington and, again, will be played behind closed doors.
The spokesman said they would wait for government advice on whether crowd restrictions are to be lifted before deciding if there will be spectators at the final game of the series in Tauranga on Sunday, March 7.
Sport is not allowed under Level Three and Ardern's snap decision meant it was unlikely the start of the America's Cup final between holders Team New Zealand and Italian challengers Luna Rossa would go ahead on March 6.
In Super Rugby Aotearoa, the Waikato Chiefs play the Otago Highlanders in Hamilton on Friday, while the Canterbury Crusaders host the Wellington Hurricanes on Saturday with both matches presumably in empty stadiums.
The Auckland Blues celebrated beating the Wellington Hurricanes in Wellington on Saturday and then faced the prospect of finding a new short-term home.
Although they have a bye next week, coach Leon MacDonald said if they returned to Auckland, they would not be allowed to train.