A Canterbury high school student has tested positive for coronavirus.

A student at Kaiapoi High School received the positive Covid-19 test result today as the Ministry of Health urgently tracks and traces contacts.

They have also been in contact with others diagnosed with Covid-19, the school told parents and caregivers this afternoon.

"Health authorities have been working with the school and family," principal Bruce Kearney said.

Parents and caregivers were first emailed yesterday afternoon with "some bad news" from Kearney.

"We currently have a person awaiting Covid-19 test results and we are taking a precautionary approach to managing this," he wrote.

Kearney confirmed to the Herald this morning that it was a student who was being tested for coronavirus.

"We are a strong community and we will get through this," he said.

New Zealand now has 155 cases of confirmed and probable cases, with 40 new cases confirmed today, as the country moves into lockdown at 11.59pm tomorrow.

The Ministry of Health contacted Kaiapoi High, which has a roll of nearly 900 pupils, yesterday afternoon.

Ministry officials requested that all "staff and students need to go into isolation effective immediately" for the next two weeks.

It is more than the mandatory isolation that all New Zealanders will be experiencing from tomorrow – with self-isolation meaning that even in the home, people need to separate themselves from those they live with as much as possible and limit contact with people other than the people they're self-isolating with.

"I know that this is not the news that you will want to hear. This affects a large group of our community," Kearney says in his email seen by the Herald.

"My heart goes out to you all at this difficult time."