Logan Park High School in Dunedin is closing for at least 48 hours after one of its students tested positive for coronavirus.
It means New Zealand now has 12 confirmed cases of the disease.
The student is the son of a Dunedin man who contracted COVID-19 after returning from Europe.
He developed symptoms after he returned to New Zealand. Later on, two of his family members were also showing symptoms. All three people are currently in self-isolation.
The school's co-principals, Kristan Mouat and Peter Hills, told parents about the positive diagnosis in a letter on Tuesday, Stuff reports.
The Ministry of Health said in a statement that the school is working with education staff and health officials.
"The school is to close for 48 hours while close contacts are traced and put in self isolation and is monitored by health officials daily. Other contacts will be given advice about what to do if they become unwell. The school will be carefully cleaned before reopening," it says.
The school will not reopen until it is cleared to do so by health officials.
"The Ministries of Education and Health are working closely with public health services in Dunedin and the school to help minimise disruption, progress contact tracing and reduce the possibility of spread," the statement says.
The Ministry of Health's Director-General Dr Ashley Bloomfield said earlier on Tuesday that since the man, who is in his 40s, showed symptoms five days after returning to New Zealand, there is no need for contact tracing for people who were on his flight.
The Ministry of Health announced three new positive cases earlier on Tuesday.
Aside from the Dunedin man, the other two new cases are a man who is in his 30s and his father who is in his 70s. The younger man became unwell on the flight and his father felt ill the following day.
Neither require hospital care and they are both recovering in Wellington.
They travelled on American Airlines flight AA83 from Los Angeles to Auckland, arriving on March 14. They sat in seats 4A and 10H. They then flew to Wellington on flight NZ419 that same day and their seat numbers were 1B and 1C.
The Public Health Unit and Healthline have been contact tracing passengers who were sitting near them on both flights.
Dr Bloomfield added they are expecting "more sporadic" cases of COVID-19.
"All our cases to date are associated with international travel. And, as over the last two weeks we have seen a big increase in the number of countries overseas with cases, we will expect more travellers returning to New Zealand to present with symptoms of COVID-19."