Some teachers are feeling angry and unsafe because of the risk of catching Covid-19 in their classrooms.

Teachers who contacted RNZ to comment on a story about high rates of Covid-19 infection among school staff say too many students were not wearing face masks.

They say the government should not have left schools to decide how they would restrict the spread of the virus.

A relief teacher who worked across several schools said her risk of catching Covid-19 varied from school to school.

"It feels like you're playing Russian roulette with your health because you don't know what you're going to be encountering. Schools are not universally endorsing mask wearing so I've been in some schools where only a handful of staff and students are wearing masks," she says.

"I've been to a school where they've got a pool on which staff member is going to be infected next."

Several teachers said they bought their own KN95 masks because they were safer than those provided by the Education Ministry, and one said he had also purchased an air purifier for his classroom because the school had been supplied with only one.

"I am nervous and a lot of staff are nervous," he says.

"Essentially our future lives, the potential to get disabled through long Covid is in the hands of teenagers or children to decide, because the decisions they make about coming to school, wearing masks and so on and so forth are the decisions that make our risk profile," he says.

Other teachers who contacted RNZ said Covid-19 was having a big impact.

"It's miserable! Very few students are masked and most teachers have given up on wearing them. We have no relievers left and teachers are giving up their free periods to cover sick teachers. A student teacher is doing unpaid relief," wrote one.

Another teacher warned that even when face masks were encouraged, many young people did not wear them.

"Probably around 50 per cent of students wear masks in class. It feels unsafe, probably because it is unsafe. Our protection: we open doors and windows. We wear masks. Students are 'strongly encouraged' to wear masks," they wrote.

One teacher says they resigned because the government removed its mask mandate and another told RNZ they and others were thinking of doing the same.

"There's definitely a group of us at my school who are looking at resigning because we don't feel safe going to work. There is a real split between staff and those who feel unsafe in assemblies etc. where there are not many masks are definitely disadvantaged," they wrote.

Another says Covid had made work much harder.

"Long days, lots of relief teachers, meetings being repeatedly bumped, kids missing heaps of school, trying to plan when we don't know what the heck will happen next, and on top of all of this I'm bloody freezing from the state-of-the-art ventilation system (open windows & doors)," they wrote.

Other teachers said Covid prevention measures appeared to be working in their schools.

"I caught it from my 15-year-old instead of my primary class, because I strongly encourage masks. Surprise! Now that college is back to compulsory masks after a two week shutdown," a teacher wrote.

"At both schools I work at several teachers have gone down with Covid amidst this second wave. I'm thankful that staff at both schools are excellent with their mask wearing. Big ups to the kids too! Teaching with all doors/windows open in winter terms is tricky but worth it," wrote another.

Teachers told RNZ they were worried by the lack of air filters in their classrooms.

They also warned that some schools have trustees who actively opposed measures aimed at controlling the spread of Covid-19 and the government needed to be more active.

Their comments followed an RNZ report on figures indicating teachers were catching the coronavirus at a rate of about 16-17 per thousand per week, compared to about 11 per thousand in the general working age population.

Teachers were in an impossible situation, employment law specialist Jennifer Mills told Morning Report.

There were Covid-19 control mechanisms forming part of an employer's obligations to provide a safe and healthy environment and if these weren't being followed Mills advised teachers to speak up.

"It's been made very difficult for everyone, given the lack of government mandate for students to wear masks. But the question that has been put to me was whether boards of trustees can lawfully and reasonably require employees to return to work now," she says.

"Every employer has an obligation to provide a safe and healthy working environment and to take reasonably practical steps to do so, and in the teaching education environment masking-wearing is best.

"We can ask students to wear masks. Junior school makes it much more difficult because kids are sick of it... as well as washing hands, distancing and of course having doors and windows open, which is not ideal in winter when there are other viruses running amok through the school.

"But teachers have a right to a safe working environment. I would have thought that principals and boards would be supportive of an arrangement where students are asked to wear masks..."

John Gerritsen/RNZ