The Mental Health Foundation says new armed units being trialled by the police will result in people experiencing mental health crises being shot.
Special patrol vehicles carrying armed officers are to start patrolling Counties Manukau, Waikato and Canterbury as part of a six-month trial to cut down response times to serious incidents involving firearms.
The armed response teams will be made up of police staff who are part of the armed offenders squad (AOS).
The AOS is normally on-call 24/7, but for the trial they will be routinely armed, equipped, and mobile.
Mental Health Foundation chief executive Shaun Robinson said the organisation sounded similar warnings a decade ago when tasers were introduced.
"These warnings were not heeded. In 2016, police officers were found to have discharged tasers in 25 percent of all cases involving an individual with mental illness, but only 16.6 percent of cases involving others. Recent figures indicate this trend has continued.
"This is an urgent concern and so far, we have had no indication that the safety and well-being of people experiencing mental distress has been considered by those leading the trials. There is no doubt that more armed officers will result in more deaths and injuries for people experiencing mental health crises. Now, as well as shooting people with tasers the police will be shooting them with guns."
Mr Robinson added that because Māori and Pacific people have higher rates of mental illness, they'll be shot more often.
"While the New Zealand police have acknowledged racial bias against Māori, this acknowledgment has had no impact on the number of Māori being arrested or approached by police, and two thirds of individuals shot by police in the last decade were Māori or Pasifika."
He said all the evidence showed that people with mental health problems were not more prone to act violently and were, conversely, more likely to be victims of violence.
"We cannot keep saying we want to normalise mental health, want people to share their experiences and ask for help while implementing policies and practises that undermine their safety and their human rights," Mr Robinson said.
Announcing the new police squads on Monday, Police Commissioner Mike Bush said armed response teams were a standard feature of policing internationally.
"The police's mission is that New Zealand is the safest country. Following the events of March 15 in Christchurch, our operating environment has changed.
"The threat level remains at medium and we are continuously reviewing our tools, training, and capabilities we use to provide Policing services to ensure we remain fit for purpose."
Police Minister Stuart Nash said the trial did not mean the police were moving to routine arming.
The trial of the new teams would be closely monitored, he said.