Director-General of Health Dr Ashley Bloomfield is remaining cautious despite close contacts of the latest Covid-19 community cases returning negative tests so far.
Three new cases were confirmed yesterday in South Auckland - a woman, her husband and their daughter. A fourth member of the household has so far tested negative for Covid-19.
Within the last day, 1017 people were tested for Covid-19 within New Zealand and not linked to the border, according to the Ministry of Health.
All returned negative results, including close contacts.
Bloomfield says the lack of further community cases is an "encouraging sign".
"But it's the days ahead that will be crucial as results from expanded testing across the Auckland region and the Waikato and Taranaki start coming through," he told media at the post-Cabinet press conference today.
"What we really want is that the results of this testing at [Papatoetoe High School], at the workplace and in the wider South Auckland community to rule out that there is an onward transmission or rather undetected transmission."
An investigation is still underway as to how the family contracted Covid-19.
Genomic sequencing confirmed they have the highly infectious UK variant of the virus.
Further work is being carried out to see if their strain of the virus matches any identified cases in managed isolation or quarantine (MIQ) in New Zealand, or any strains in the global genome database.
The woman works for an airline laundry and catering company, but the Prime Minister says that doesn't mean she contracted the virus there.
"The most likely assumption that everybody jumps to is the fact there's some connection here through a workplace at the international border being involved, in a worker connected to that wider workforce," Jacinda Ardern says.
"However, we don't want to miss anything and that's why we continue to treat one other member of the household as being potentially the index case, just to make sure we don't miss anything - that's what our cautious approach requires which is why that testing around the high school is just so important as well."
Auckland is currently in Alert Level 3 lockdown until 11.59pm on Wednesday, with the rest of the country in Alert Level 2 until the same time.
The Alert Levels are due to be reviewed every 24 hours, meaning the lockdown may be cut short or it could be extended.
Ardern admits we may never confirm the source of the outbreak.
The largest Covid-19 cluster was in August, the index case believed to be a man working at an Auckland cool store facility.
Authorities ruled out the possibility of surface transmission but the official source of the outbreak was never confirmed, though a breach at the border was highly speculated.
"We have certainly in other scenarios developed strong theories, but we haven't always been able to nail down with 100 per cent assurance that that was the exact place it happened," Ardern says.
"That has not stopped us from being able to have enough confidence that it's been contained."
Addressing testing, Ardern is pleading for people to stay home if they're well and haven't been to any of the locations of interest released by the Ministry of Health.
Some people have reported waiting three hours for testing.
"At these times we do get heightened demand, again we just reissue that plea, if you're not symptomatic, if you're not unwell and you haven't been to any places of interest, we are not asking you to come forward and be tested," Ardern says.