The Ministry of Health has revealed there are five confirmed COVID-19 cases at Auckland's Marist College.
Director-General of Health Dr Ashley Bloomfield said on Wednesday that all students and staff are being treated as close contacts, meaning they're in self-isolation for 14 days.
"Staff and students should not congregate with anyone outside their home. They will be in the same boat as all New Zealanders from midnight tonight [Wednesday]."
The Mt Albert school has been closed all week after a teacher tested positive for the virus on Sunday.
Dr Bloomfield says there are "a number" of staff members who are being tested for the disease after they started showing symptoms.
There were a further 50 confirmed and probable COVID-19 cases on Wednesday, bringing the total in New Zealand to 205.
Dr Bloomfield warned that even though the country is going into lockdown at 11:59pm on Wednesday, there will still be a rise in cases "for at least 10 days".
"That is because the infections we are finding today, and over the coming week to 10 days, are people who have been infected before today. So the numbers will continue to increase before they turn around," he said.
A total of 22 people in New Zealand have recovered from COVID-19.