Auckland's Marist College for girls has confirmed three new cases of coronavirus COVID-19.
In a letter to parents, principal Raechelle Taulu said all staff and students at the college were considered close contacts.
The letter says families need to assume their daughter has been in contact with someone who has the virus.
"However, this does not mean that your daughter will get the virus, yet we have a duty of care to inform you.
"If your daughter tests positive for COVID-19, I ask that you please let the school know
"It is critical that families follow the Ministry of Health guidelines for isolation and testing."
Taulu encouraged students who were well to continue their learning online. The school closed earlier this week after a staff member tested positive for COVID-19 and all New Zealand schools will close at midnight on Wednesday.
Prime Minister Jacinda Ardern announced on Monday New Zealand was moving to COVID-19 alert level three for 48 hours, before moving to level four - effectively placing the country in lockdown.