A woman has just tested positive for Covid-19 despite flying back to New Zealand more than two weeks ago.

The woman, in her 20s, is one of two new confirmed cases of the virus announced today.

She travelled from the United States to New Zealand, arriving on April 25, and is in the Counties Manukau DHB region, according to the Ministry of Health.

Her positive test came back on Saturday, 15 days after arriving in New Zealand - meaning she may have been out of quarantine for several days while still testing positive for the virus.

A list of confirmed cases on the Ministry of Health's website said she had arrived in the country on March 25 but the ministry has since confirmed that date was incorrect.

The Herald has asked for more information on the case including whether she was in quarantine, when she was tested, when she developed symptoms - if any - and if the test was a "weak positive" test, or thought to have come in the late stages of her illness.

The average incubation period for the virus that causes Covid-19 is thought to be about five days. But there are reports of some people receiving positive tests for the virus long after they are thought to have recovered.

The case follows the announcement this week that a Marist College student had just received a "weak positive" confirmation that she had the virus, despite a cluster breaking out at her school over a month ago.

It was thought she was in the very late stages of her illness and was no longer infectious.

The second case confirmed today was linked to the St Margaret's Hospital & Rest Home in Auckland.

The person is not a healthcare worker - they are a household contact of an earlier case linked to St Margaret's. They have been in self-isolation since that case was notified.

There was no press conference held this afternoon but the details were released in a Ministry of Health statement.

Two people are hospital and there are 102 active cases across the country. There have been a total 1494 cases - 1144 confirmed and 350 probable.

The past three weeks have single-digit case numbers each day, with two days in a row of zero cases in the past week.

This is the final release of public data ahead of Cabinet's decision tomorrow on when to move down to level 2.

On Wednesday a student at Marist College was reported as testing positive for the virus, despite the Auckland school's Covid-19 cluster breaking out more than a month ago.

Since then all students have supposedly been in self-isolation and lockdown. The student in question had only had one symptom - a loss of smell - and they weren't aware they had the virus until Marist College students went for widespread testing.

Director-general of health Dr Ashley Bloomfield said that test was a "weak positive" so it was almost certainly very late in their illness.

But the significance of the weak positive test so late was not fully understood.

He said it was unlikely the student was still infectious, but they would remain in isolation and be tested again next week.