Mental health or emotional distress is a factor in almost a quarter of cases where police dog bites leave people needing hospital treatment, police figures show.
The information, obtained by RNZ under the Official Information Act, revealed police dogs bit people more than 1200 times in the past five years, with 10 percent of those bitten ending up in hospital.
A summary of bites needing hospital treatment showed suicide threats, mental health issues or emotional distress were a factor in almost a quarter of such incidents.
Police have defended the numbers, saying dogs are never used lightly, but advocates say the trauma exacerbates an already delicate situation.
Police dogs national co-ordinator Inspector Todd Southall said dogs were only deployed when needed.
"It's not what we want to [deploy them], because we're here to actually protect and look after our community.
"Having said that our dog handlers are probably dealing with the most violent, dangerous and drug-fuelled members of our society on a day-to-day basis and at times we're going to have to use force and we have to use our police dogs - that's just the reality of the situation."
Police Conduct Association president Shannon Parker said the use of dogs in mental health call-outs needed close scrutiny.
"It's troubling to think police could be called out to prevent a self-harm incident and the result of that call-out is the person could be hospitalised because of police actions. It seems to defeat the purpose."
Mental Health Foundation chief executive Shaun Robinson agreed.
"Violence in response to a mental health situation or a suicide [threat] situation is just not okay," he said.
Police had made great strides in how they dealt with mental health call-outs but there was more to be done, Robinson said.
"This is part of a bigger system of how we respond to mental health issues," he said.
"A lot of people are not getting support early enough so a lot of these crisis situations that play out with the police could be avoided."
Southall said mental health responses were among the most stressful situations officers faced.
"At the time a dog handler is facing a mentally disturbed person who may have a weapon, maybe trying to harm himself, other people or the police officers or the dog handler concerned, we've got to deal with that situation as it evolves in front of us," he said.
"When we're facing some of these situations they are critical, critical incidents and the handlers have to make a decision."
Police Association president Chris Cahill said officers were left in an unenviable position dealing with tens of thousands of mental health call-outs a year.
Training in handling such situations was always improving, but police should not be the de facto frontline officers in responding to mental health crises.
"I certainly think the best investment is in frontline mental health resources," Cahill said.
"Getting those experts out, whether it's with police or by themselves, that can try and de-escalate things at the earliest possible occasion.
"Many of these people that get violent have actually interacted with police on many other occasions but they haven't been able to get that long-term help."
Investment in mental health care was key, Cahill said, but it was a reality that dogs would always be a necessary tool when officers were facing weapons and violence.