This would be re-accessed on Monday, Ardern said.
Ardern warned South Islanders the decision could change if any evidence emerges of Covid-19 transmission before Monday.
"We absolutely still want symptomatic people tested. If we see any evidence that we have made the wrong call in where we move, we will change that decision."
Alert level 3 would be reviewed weekly for New Zealand south of Auckland and no decision had been made about when there would be a move to alert level 2.
Meanwhile, Ardern said Northland and Auckland would likely stay at alert level 4 for another two weeks.
The decision was made to extend alert level 4 for four days in the South Island in part because of the positive wastewater test in Christchurch, despite this being seen as likely linked to Covid-19 cases in managed isolation in the city.
The cases in Wellington, and reaching the full two-week cycle of the virus were the other two reasons Ardern cited for extending alert level 4 until Tuesday for New Zealand south of Auckland.
Northland was included along with Auckland as being likely to remain in alert level 4 for longer than the rest of New Zealand in part because of the case in Warkworth.
"It's likely Auckland will remain at level four for a further two weeks," Ardern said.
When Auckland settings were confirmed on Monday, an update for Northland will be provided.
The additional four days in alert level 4 for the whole of New Zealand gives health experts a full 14-day cycle of data and information since the country went into lockdown on Tuesday night last week.
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Disappointment from hospitality businesses in South Island
The Restaraunt Association has said South Island hospitality businesses hopeful of a move of alert levels this weekend will be disappointed by the extension.
"We urge all of those hospitality businesses that are doing it hard right now, to stay strong and seek out help," said association CEO Marisa Bidois
"Our most recent feedback from members shows that whilst they largely support the level 4 lockdown, 75 per cent of those businesses wouldn't be financially viable after two weeks at this level."
Bidois said they have heard from several members saying they had only just made their final repayments on loans from the 2020 lockdowns so they're devastated they're back in that position of starting the process again.
"Most people will understand just how challenging level 4 is for any industry that can't work from home. For businesses owners, it means no revenue at all which is very stressful when you have bills to pay
"Many hospo people are social people and the isolation of being at home unable to work is really tough for them right now so we know how many of them are just looking forward to firing up their ovens and coffee machines and being able to serve people again," she said.
Police to monitor borders
No regional travel is allowed through level 4 regions, except those who need to travel for work or someone with an exemption.
Police will enforce boundaries and check on exemptions when south of Auckland moves to level 3. The same boundary used in February will be used again.
MBIE will be open for applications from Sunday for people who need exemptions to cross boundaries for work.
What level 3 means
Level three allows us to give businesses and others more freedoms but contact with others needs to remain limited, she said.
"We want you to limit contact as much as possible," Ardern said.
She said takeaways can only be operated through contactless methods.
"We want you to limit contact as much as possible."
Public venues remain closed. Groups of 10 for weddings, funerals and tangi are allowed.
Masks are still mandatory on all public transport and it is encouraged to wear one in public spaces as you can.
PM says lockdown is working
Ardern said lockdown was working.
"We have evidence that what we are doing is working, but caution is still required.
"By far the most effective tool we have right now is level 4."
There would continue to be further cases as household contacts tested positive for Covid-19.
Friday saw a new record number of daily cases declared, with 70 recorded on Friday, bringing the total number of cases in this outbreak to 347.
The press conference follows a Cabinet meeting where ministers will decide whether parts of the country outside Auckland are able to move down from alert level 4, down the alert level scale.
The decision is a difficult one; while the outbreak has not yet reached its peak, it appears to be concentrated in the Auckland region. The total number of community cases in Auckland is 333.
The only other part of the country with cases is Wellington, which has recorded 14 cases so far, with one new case added on Thursday.
Before moving to a more permissive alert level, the Government wants to establish clear links between each of the cases in the outbreak. This gives an idea of how far the virus might have spread.
So far, 278 cases have been epidemiologically linked to another case or sub-cluster, while 69 have links that have not been established.
More MIQ space
Ardern said there are 274 rooms designated for quarantine across the country.
She said family members are giving each other Covid when they are asymptomatic.
Extra MIQ facilities have needed to be brought on for contacts of Covid cases in Auckland.
Bloomfield said it didn't present any further risk for people to be isolating from home.
However, he said bigger families were prioritised to be moved to other facilities as it was harder for them to isolate in the same house.
Positive worker at Warkworth rest home
Asked about the rest home positive case in Warkworth, Ardern said the worker was fully vaccinated and those facilities were prioritised for testing.
The staff member at the Amberlea Home and Hospital Care Facility in Warkworth worked two shifts while infectious in the facility's dementia ward.
However, that staff member is fully vaccinated and adhered to strict Infection, Prevention and Control protocol, including wearing face coverings and other PPE.
Experts urged caution
Most experts believe the latest outbreak could drag on for some time.
Experts are urging a few more days in lockdown across the country as part of a "cautious approach" to containing the Delta outbreak.
And the Government's top adviser says while "I'd love to say Santa Claus exists" there was no easy way to stamp out Delta and there were still tough times ahead.
Epidemiologist Dr Michael Baker said there was still a risk the virus could be incubating outside Auckland and Wellington.
Level 3 was good at containing spread, but not at eliminating the virus, Baker said.
Bar any developments, a "cautious" approach could see the South Island enter level 3 from Tuesday, meaning it had been through a full 14-incubation period since the lockdown began.
Level 3 included opening up gatherings to 10, and limited hospitality services, but still prevented large gatherings including most businesses and schools.
"It is feasible [to go to level 3] from this weekend, but carries more risk," Baker said.
It was also feasible the North Island, bar Auckland, could also be lowered to level 3 then, but there remained some risk given the 12 cases in Wellington.
The fact they were all contained in their bubbles and there had been no spread was reassuring, Baker said.
"One option could be for Wellington and/or the North Island to hold on a bit longer, and then effectively split the country into three zones with Auckland."
More information about cases that were already effectively quarantined, in their bubbles, and those that were out in the community needed to be provided, Baker said.
If there was a move down alert levels, Baker said the Government should look to carry mandatory mask use in certain crowded indoor levels with it.
Eminent epidemiologist Sir David Skegg says he is cautiously optimistic New Zealand will get out of this outbreak - but it all depended on the community's ongoing response.
He said on current progress, he expected the country to emerge from lockdown in a few weeks.
But Skegg, the Government's adviser on elimination, told Newstalk ZB's Mike Hosking that even with vaccination levels up, public health measures would still need to be maintained with Delta.
"Unfortunately there's no easy way out of. I'd love to say Santa Claus exists but unfortunately whatever we do in New Zealand we are going to have some tough times ahead."
Skegg maintained elimination remained the best option for New Zealand. "No one would have wished to have this outbreak but the good thing is that it is making people realise we need to get vaccinated," he said.
"I'm cautiously optimistic that we will get out of this but Delta is definitely a lot more infectious, it's a lot more difficult to stamp out and it really all depends on us," said Skegg.
"If we observe the lockdown better than Melbourne and Sydney have done then, of course, we will get rid of this in the next few weeks ... I'm expecting this to happen."
But there are some shoots of hope.
Bloomfield has said the numbers this week show the growth in cases is not exponential.
That means while the number of new cases is increasing each day, cases are not exploding.
"The good thing about this is while this is a steady growth, it is not exponential," Bloomfield said, updating case numbers this week.
"We do know that our actions to slow and spread the virus will begin to see a slowing of those numbers increasing. And, indeed, the fact that the rate of increase is not exponential is explicitly because we have alert level 4 in place," he said.
However the enormous number of contacts in this outbreak is testing the small army of contract tracers, which is soon expected to number 1200.
As of this morning of the 629 "close plus" contacts, 85 per cent had been contacted, 63 per cent have had results - 15.6 per cent tested positive.
Of the 24,541 close contacts, 68 per cent have been contacted, 75 per cent have results and just 0.3 per cent have tested positive.
And of the 1,235 casual contacts, 47 per cent had been contacted, 69 per cent have had results, none of which were positive.
The latest outbreak has so far claimed no fatalities. Nineteen of the current community cases are in a stable condition in hospital; one of the cases is in a stable condition in ICU. Of those in hospital, two are in North Shore Hospital, eight are in Middlemore Hospital, and nine are in Auckland City Hospital.
There are also signs of optimism with the nation's vaccine rollout, which has broken multiple records this week - although New Zealand's rate of vaccination remains well behind the rest of the world.
There were 90,757 jabs administered yesterday.
Of these, 65,541 were first doses and 25,216 were second doses making it the biggest daily total to date.
More than 3.11 million doses of the Covid-19 vaccine have been given so far and of those, 2 million were first doses and more than 1.1 million were second doses.
With ODT
Comments
Called it!.
Have a biscuit.
It surprises me given you have been anti every step that has been taken so far.
It was an easy call. TAB wouldn't have offered odds on it.