Five members of the same family who are connected to Avondale College are among the new Covid-19 cases confirmed on Thursday.
It comes after a teacher at the secondary school caught the Delta variant.
Avondale College Principal Lyndy Watkinson told Checkpoint about 2800 students and staff are considered close contacts and are now in isolation for 14 days.
"We're a big, busy secondary school, so in a community such as ours we're treating all students and staff as close contacts.
When the lockdown announcement was made on Tuesday, a group of students were in Rotorua for the Cadenza Big Sing event with other schools.
That connection has left other Auckland schools racing to have their students tested.
Thousands of Auckland school students have been mingling with Avondale College students over the weekend.
"Auckland is a small place... and certainly in a secondary school environment," Auckland Grammar Headmaster Tim O'Connor told Checkpoint.
"We're certainly thinking of Avondale College, the staff and students, and offer them out full support.
"We've got a range of connections with Avondale, we have a great working relationship with them, and of course some of our teachers have partners who are teachers at Avondale. .
"Over the weekend some of our students competed against Avondale groups, starting with Cadenza Big Sing Festival in Rotorua.
"There were twelve choirs, seven other schools from Auckland, one from Tauranga, one from Hamilton, one from Rotorua.
"We also competed against Avondale at the Auckland Jazz Festival on Sunday, where there were about 50 bands competing. So lots of connections."
O'Connor said the school has talked to the organisers of those groups and parents, encouraging them to get tested if needed and follow Ministry of Health guidelines.
He said he has not heard any specific advice from the Ministry of Education or Ministry of Health.
"We've just tried to be proactive and follow what we're hearing via media announcements."
Vaccinations for children 12 years and older
O'Connor said the move to vaccinate people from 12 years or older is a "great thing".
"We know that this Delta variant is affecting people of all ages, so the sooner we can vaccinate the entire population, the better, and I I think we should do so with some real haste.
"We're working immediately to try and get all our staff vaccinated.
"So we're working with a provider to see if we can get them to come on campus to be able to do that for staff, and in particular, once we've talked to parents of boarders, to get our borders vaccinated, because they live in a communal environment."
