In the Auckland Central police district, the initiative began on November 30 and has seen on average two people each day taken to the Auckland City Hospital emergency department instead of being detained in a police cell until medical staff are able to assess them.
Auckland district commander Superintendent Richard Chambers said the change meant not only did people get better care, but police staff were able to spend more time on the frontline.
"There aren't too many people who haven't got someone reasonably close to them who hasn't to some degree experienced the effects of mental illness and because of that, most people can relate to how important it is that people who are unwell get the right treatment," he said.
The police had worked closely with the Auckland District Health Board this year on a new process under which people in distress would be taken to "the right place" quickly and got the right treatment from medical practitioners.
Mr Chambers said there has been some "teething issues" with wait times for patients, but the benchmark was assessment conducted within one hour of presenting at the hospital's emergency department.
Police officers waited with patients until they were seen, he said.
The Auckland District Health Board mental health and addictions director, Dr Clive Bensemann, said the change had been years in the making.
"We've been working hard on getting the best outcomes for our patients, while acknowledging that the police have a number of challenges in this area of policing.
"Our emergency staff also face challenges here and the work has focused on good outcomes for patients and prudent risk management for staff from both services."
Mental Health Foundation chief executive Judi Clements said the initiative came after repeated comments from the Independent Police Conduct Authority.
"The IPCA really have commented how unsuitable it is for someone who's in distress to be in a police cell; it's not really acceptable.
"It can only be a good thing if people are in a more therapeutic hospital environment, where it's about help and not custodial."
Following a review of 31 complaints and incidents referred to the IPCA in the past three years, a report in March criticised the police practice of detaining people with mental health issues.
In his findings, IPCA chairman Judge Sir David Carruthers said: "While officers try to deal with them patiently and professionally, the prisoners' mental distress is often made worse and they sometimes suffer long-term harm.
"Unless a person experiencing a mental health crisis is violent or poses an obvious and immediate threat to the safety of others, all practicable steps should be taken to avoid having them in police cells."
The new system has been used in other districts, including on the North Shore, but exact figures will not be known until 2016, said a spokeswoman for police national headquarters.
"Police and DHBs across New Zealand are working together to ensure the best possible outcomes for people who are experiencing mental distress and part of that work is to make sure mental health assessments take place in the right environment."
