New Zealand is entering its second day at heightened alert levels after four people in the community tested positive for Covid-19.

New Zealand has four positive cases and four probable cases of Covid-19 outside of a managed isolation or quarantine facility.

This morning Mount Albert Grammar principal Patrick Drumm told Morning Report a student from the school tested positive for Covid-19.

Director-General of Health Ashley Bloomfield confirmed that the student was a close contact of the four exisisting South Auckland cases.

He says the school told staff, parents and students last night after they were made aware of the result.

Mount Albert Grammar is one of the biggest schools in the country.

There was no link to the border or to managed isolation or quarantine facilities, prompting the government to activate its resurgence plan. Auckland moved to alert level 3 at midday yesterday, while the rest of New Zealand moved to level 2.

While the new restrictions are in place until at least midnight on Friday, there are warnings New Zealanders should prepare for them to remain in place beyond then.

Police set up checkpoints around Auckland's border, testing has ramped up, and people rushed to the supermarket to stock up.

National Party leader Judith Collins has called for the election to be postponed until at least November, but Ardern has said her focus right now is on the response to the new cases, not the date of the election.

Dr Bloomfield announced yesterday that one person in managed isolation had tested positive while four people were being treated as probable cases. They are all linked to the family who tested positive, are symptomatic and are in isolation. They have all been tested.

Dr Bloomfield also issued an order to all the colleagues of the people who have tested positive, and the people they live with. They are all to isolate until they are contacted by health officials and given further instructions.