Principals and early childhood centres are worried they will break the law if they stop parents from collecting their children during emergency lockdowns.

They want guidance from the Education Ministry following an independent review of the lockdown of 221 Canterbury schools after 51 people were killed in two mosque attacks on March 15.

The review by KPMG says some schools faced aggressive and even violent parents determined to remove their children from classrooms that were locked-down for up to four hours.

Principals were not sure what their legal position was and Shane Buckner from the Canterbury Primary Principals Association says they had hoped for advice in the report.

"When you do have someone who definitely wants to take their child away, what is the legality of that, and I know the ministry are still working on finding out," he says.

"People want to look out for their child, but at the same instance the community needs to know what is appropriate and what needs to be done."

Shane says the report noted that schools were less safe if they opened their doors to allow some parents to remove their children.

Kidsfirst Kindergartens chief executive Sherryll Wilson says it's seeking legal advice while it waits for the ministry to provide more information.

"It's a fine juggling act in our responsibility to keep staff and children safe against balancing the rights of parents if they wish to take their child out of our early learning centres," she says.

"What risk does that pose not only to their child but also to other children and staff should they do that. We are looking for further clarification from the ministry on this."

The ministry's deputy secretary sector enablement and support Katrina Casey says it was still considering what to tell schools and early childhood centres and in the meantime they would need to weigh up competing demands and rights.

"Parents do have a right to take their child out of school should they wish to do but, again, safety of the child is really critical and that's something while on school grounds that a principal is going to assess," she says.

Katrina says schools that kept all their parents informed during the Christchurch the lockdown were less likely to have parents trying to break it.

She says the ministry had been asked to advise on several other grey areas.

"For example, if children or young people were off-site and then came back to the school, is the school required to let them back in. There's some things around technology, for example the mobile phones, devices and tablets ... in an emergency situation should those be taken off children?"

Secondary Principals Association president Deidre Shea says while principals waited for advice from the ministry, they would be sticking to what they had been told by police and security experts.

"The advice is very clear - if you're in lockdown you're in lockdown; you don't come out, you don't do anything until you have been advised you can do so by authorised personnel," she says.

Canterbury West Coast Principals Association president Phil Holstein worked on the review and says an important recommendation was better guidelines for parents so they understood how lockdowns worked.

He says parents needed to "trust the fact that in these situations that teachers are looking after their children".

Phil says schools generally did a good job of managing the lockdown.

New emergency alert system

The Education Ministry has launched a new emergency system for contacting schools and early childhood services during an emergency.

Katrina says the system called Mataara allowed the ministry to send text messages to mobile phones of designated staff in schools and early childhood services nationally or in a particular region or area.

"Literally we press the button and they will receive an automated message," she says.

Katrina says the ministry had been developing the system for use during extreme weather events but fast-tracked it after the March 15 attacks.

"We have all the contact details for all schools so we've loaded them into the system. We are just checking to make sure that we've got the numbers that schools want a message like that to go to," she says.

Katrina says schools and early childhood centres could use the system to respond to the ministry and indicate if they were open or closed or if they needed help.

Education Minister Chris Hipkins says overall schools acted professionally and tried their best, but there was a lot to be learnt.

"There does need to be greater clarity clearly about the relationship between parents and the school in a lockdown situation. Clearer advice to parents, clearer advice to schools about what to do for example if a parent arrives and says 'I want to take my child'."

Chris says many schools had no experience dealing with that type of situation.

"It's the first time we've ever encountered something of that size and scale... for many of them they were dealing with that for the first time."

He says every school should be able to have a reliable communication system.

"Mass communication isn't that expensive when you've got the right people loaded into the system."

-RNZ/John Gerritsen.