Central district police requested trauma counselling more than 350 times in the last five years.
Documents released to the Chronicle under the Official Information Act reveal the extent of work-related trauma and occupational stress for police employees.
Since 2011, 354 officers attended counselling or received psychological support to manage the effects of traumatic experiences.
Ninety-nine requested support last year.
According to the former chair of the Police Association's central district, the numbers reflected a growing awareness of the need for psychological support for officers.
"It's an improving attitude. [Before the mid-2000s] no one ever went to see a counsellor or get independent psychological advice regardless of the number of incidents they were involved in," said association vice-president Luke Shadbolt.
"It's a good, positive step - looking after the emotional health and psychological welfare of police staff."
Mr Shadbolt said Whanganui had a particularly high rate of family violence, gang activity and road accidents. "Those are all incidents where you're dealing with other people's emotions on a very regular basis, and dealing with them in a very raw state ... You try to stay impersonal and try not to get emotionally involved, but over a period of time you can't help [it] - those kinds of things build up."
Mr Shadbolt said mental harm was not only caused by significant, traumatic incidents, but by everyday exposure to smaller events.
"There is a significant cumulative effect of attending what appear to be day-to-day incidents that police always deal with, but in reality they all take a little bit of an emotional and psychological toll on you," he said.
"We talk about the emotional bucket which fills up over time with little drips, and eventually it will overflow.
"We actually see that happen quite a bit."
He said counselling was often mandatory for officers involved in particularly critical events, such as the Christchurch earthquake, but was available to officers by request at any time.
Since the Christchurch earthquake - after which 49 central district officers received counselling - the most frequent two months for counselling referrals were February and March 2016, when 38 officers asked for support.
Police wellness and safety manager Marty Fox said the trauma policy was available to all police employees, and was "a support system [for]... the psychological risks associated with policing generally".
Mr Fox said psychologists helped "minimise post-incident reactions and risk of developing ongoing psycho-social harm" but the support was not a replacement for good management, supervisory practices or personal coping skills.