Prime Minister Jacinda Ardern has made light of her former high school taking exception to the Government plan to have children return to classrooms next week.

"Mr Inger," smiled Ardern, when asked about principal John Inger's newsletter comments, in which he warns of the "potential disaster" of sending children back to the school once level 4 lifts next week.

He says some parents might be sending children back to school simply because they are a "pain in the neck" at home - and the Government was passing on child-minding duties to teachers.

Ardern said today she couldn't help but think Inger might have had her in mind, as an ex-student, when both her parents would have been classed as essential workers - her father was a police officer and her mother worked at the school.

Turning serious, she said she disagreed with Inger's comments.

In the three-page newsletter obtained by the Herald, Inger warned: "Children can contract Covid-19 and pass it on when asymptomatic, and they can die."

And while the school would try to maintain social distancing rules for children, this could not be guaranteed, he said.

The comments come as the Director-General of Health, Ashley Bloomfield says new outbreaks in schools are unlikely due to lack of community transmission.

Bloomfield has also said children have lower infection rates and are not as contagious but Inger said "this represents the current thinking aimed at assuring people rather than hard facts".

"Young people all over the world have been dying from Covid - they are just less likely to die than those of us who are adults, so do not think that your child could not die if they became infected," said Inger.

He said it was a "surprise" and a "concern" when Ardern announced some students would be able to return to school under alert level 3.

He said around 30 of the school's staff, or people in their bubbles, would be at "high risk" if children returned.

"As things currently stand, it seems to me that Government wants to pass on to teachers all around the country the responsibility of child-minding, in our case Years 9 and 10
students, so that more parents can go back to their workplaces.

"This ignores the potential disaster that this could result in, with our schools possibly becoming incubators for the virus.

"The students who might return to school during level 3 will most likely be the children of essential workers, and apparently also those whose parents want to send their children back to school for some reason that they do not have to explain to their school, perhaps because their children are a 'pain in the neck' at home, although there could well of course be some other good reasons to do so.

"In the former case, these students are likely to be those who are most likely to bring
Covid-19 into our school because their parents are 'on the frontline' every day and so are more likely to be exposed to the virus and infect their children when they return to their bubble."

Inger said it was his "strong recommendation" to keep children at home. He believed they were being well served by online learning.

"I can tell you that if I still had my children at school, and for those of my Senior Leadership Team who still have their children at school, we would certainly not entertain the idea of putting them at risk by sending them back to school at this time."

Ardern attended Morrinsville College and the school's 1998 yearbook famously wrote that she was the most likely student to one day be Prime Minister.

Inger also wrote: "We have yet to hear how the ministry expects bus drivers to ensure that our bus students stay two metres apart on their buses. Nor do we know if buses will be able to run as normal, as many of the Greenline Motors drivers are aged over 70 and so are very much at risk and will be required to remain at home."

The Government has been moving to allay fears about fresh Covid-19 outbreaks when schools reopen next week by saying there is very little chance of anyone with the virus being on school grounds.

That was because community transmission was all but snuffed out, which Bloomfield said was further peace of mind on the back of evidence that children were not strong vectors of transmission.

Last night the Health Ministry released a report saying that the limited health benefits of closing education institutions were outweighed by the severe impacts on health, education, economic and social inequities.

Some early childhood learning centres and many teachers are opposing the decision to open schools and ECEs up to Year 10 inclusive after the country moves to alert level 3 from Tuesday.

Education Minister Chris Hipkins said he was unlikely to force education centres to open if they didn't want to, but he said teachers should "do their bit" when asked whether they could choose to stay home.

It comes as New Zealand's coronavirus death toll rose to 13 after the death of a woman in her 70s with an underlying health condition.

She was one of six residents of St Margaret's Hospital and Rest Home in Te Atatu who had tested positive and been transferred to Waitakere Hospital on April 17.

Yesterday there were only five new cases of Covid-19, the lowest in over a month.

With 1445 cases and 1006 people recovered, the number of active cases fell to 426.

There were 12 people in hospital including three people in ICU - but none were in a critical state.

Half of the 16 significant clusters had not reported any new cases in the past week.

Bloomfield said that educators should take heart from the signs that community transmission appeared to be all but quashed.

"There's increasingly encouraging information that the likelihood of someone with Covid-19 going through the school gate is very, very low in the first place," he said.

He added that if a case popped up, close contacts should be easy to trace due to the relatively small "in-school bubbles".