More principals are leaving their jobs before retirement age and fewer experienced teachers are willing to take their place, principals' groups are warning.
The Secondary Principals Association and the Principals Federation say a principal's job is more demanding than ever and that is deterring others from stepping into their shoes.
The association has counted about 56 vacancies for secondary and area school principals so far this year, which it says was more than ever before.
However, the Education Ministry puts the number of vacancies at a similar level to previous years.
Either way, Secondary Principals Association president Sandy Pasley said, it was concerning many of the principals who were leaving were not yet at retirement age.
"We've investigated it and from what we can see, there are about 13 retiring because they're retirement age ... there's something like about 21 that are stopping being principals that are under retirement age, and some of those are going on to consultancy."
A further 10 principals had changed schools, about seven may have left New Zealand and five of the jobs advertised were at new secondary schools, she said.
The job of principal had become increasingly difficult and those who were leaving would be hard to replace.
"There's been an unwillingness on some senior managers to actually step up to the principal's role because they see the comprehensive jobs that's involved and recognise that you've got to devote the time to do it properly."
Ms Pasley says that will result in a smaller pool of applicants for many jobs and she knows of school boards that are ringing around to encourage more people to apply for their principals' jobs.
Rotorua's John Paul College principal Patrick Walsh said it was particularly worrying that some principals were retiring early.
"When asked why they're retiring it's because of stress, burnout and concerns over increased liability for principals. Examples they cite are the changes in health and safety where they face up to $600,000 fines and five years in prison, and also concerns over a more litigious environment.
"The feedback we're getting from principals is that many deputy principals and those in middle management are not considering putting their hand up to be principal."
Principals Federation president Denise Torrey said it had no figures on the number of primary and intermediate principals who had left their jobs this year, but a lot more principals were resigning mid-career.
"They're in their mid-50s and going to do other things. Principals are becoming increasingly concerned about their workloads. It's more difficult than ever to get life balance and people don't want to work that hard."
There were also more inexperienced teachers applying for and getting principals jobs, she said.
All principals needed more support, and though the Education Ministry was paying for several principal-support roles, a lot more were needed.