Papatoetoe High School principal Vaughan Couillault says the school community is hoping for the best but prepared for the worst.
The school is the exception to the reduction in alert levels announced by Prime Minister Jacinda Ardern and Director-General of Health Ashley Bloomfield this afternoon.
Students and their families are being asked to stay home, and return a negative Covid-19 test before returning to school on Monday.
"We're closed for the remainder of this week," Couillault told RNZ's Checkpoint.
"That's probably to allow the testing station to remain in play onsite unencumbered by the happenings of a large secondary school."
The pop-up testing centre at the school will remain until Sunday 21 February.
Some students would need to get retested, he said, but he did not have granular information about that.
Dr Bloomfield clarified during today's alert levels announcement that retesting would apply to classmates of the original case and teachers of those classes.
He said testing of the household contacts would take place and exposure events would be looked at. People linked to any exposure event would also be asked to isolate.
The family members for the two siblings who tested positive today - both students at the school and one of them a classmate of the student whose family tested positive on Sunday - were also isolating.
Couillault said there were some logistics to get all students tested before Monday, but "we'll get there".
He said he had not received any negative feedback about the school reopening next Monday.
Following Ministry of Health advice, he said he had not spoken with the family at the centre of the outbreak, nor contacted the new cases.
"No one wants to be pestered when they're not feeling 100 percent but also they've been moved into a quarantine facility. The public eye has been looking in their direction, we're just affording them a little space for their own wellbeing, to be fair."
The younger of the two new cases is in Year 9, in the same form and learning class as the daughter in Case A family, he said.
The second of today's new cases is the older brother of the Year 9 girl.
Couillault said he was not aware of any activities the boy might have been involved in while infectious.
"The two new cases today were not on site at school during their infectious period."
Covid-19 Response Minister Chris Hipkins told Checkpoint tonight that contact tracing had confirmed the siblings had become infected from the daughter in the case A family.
Couillault said staff at the school were prepared for any scenario that would hinder learning this year.
From tomorrow they would move to online learning.
There was pastoral care being provided.
Dr Bloomfield also confirmed this afternoon that one of the people who tested positive today works at a McDonald's restaurant in South Auckland. He said they were not symptomatic.
A household contact of the pair also tested positive this afternoon.
