It has been estimated that up to a quarter of a million children, young people and vulnerable adults were abused in state and faith-based care between 1950 and 2019.
Photo: 123RF
The findings have been released by the Royal Commission into Abuse in Care.
Of 655,000 in care during the period, it is estimated up to 40 percent were abused.
An equal number, about 254,000 were in either social welfare care or church-based care (31 percent).
There were 102,000 (12 percent) in school care and 212,000 (26 percent) in health and disability care.
The exploitation peaked in the 1970s with up to 48,000 victims in that decade
The study said little was known about the ethnicity of those abused in care.
It quoted a Oranga Tamariki report that showed 81 percent of children abused in care were Māori.
Māori children made up 69 percent of children in care.
There was also limited historical data available on the number and proportion of disabled people in institutional care.
Coral Shaw Photo: RNZ / Patrice Allen
Royal Commission chairperson Coral Shaw was astounded by the number abused and described the economic impact as eye-watering.
Taking into account the impact of physical and mental injuries, criminal behaviour, homelessness, lack of education and unemployment the estimated cost over the lifetime of an abuse survivor is $857,000 - or between $96b and $217b in total.
''These are astronomical figures beyond anybody's imagination, but they are reflected in the pain and suffering we have been hearing about. You can put a dollar figure on it, you can't put a dollar figure on the pain and suffering.''
She was amazed by the lack of record keeping of the number of children and disabled people in care during the period.
''All of this has lead to the under-estimation of the number of people affected.
''It is only when you see a number on the page like 655,000 in care that it really comes home. The extent of the issues we are looking at here.'
''I don't think any of us knew that number would be as large as it was and I think it is fair to say we were all surprised and astounded by the enormous numbers.''
Shaw said the size of the impacts both on the individuals and New Zealand society was an important message and lesson all New Zealanders had to learn.
The information would help the Royal Commission to estimate the work ahead, she said.
''So we can see how many survivors we are likely to be asked to speak to, how many investigation topics we can do and how wide and large those investigations are.''
Survivor says scale staggering
Survivor Keith Wiffin said the scale of the abuse was staggering and it made him sad - and very angry.
''Like me, I think the country will be truly shocked.
''I am sad, I am angry, I have shed tears reading these reports because this is real people's lives, but it also strongly indicates as to the scale of what is a monumental tragedy which has had a huge effect not just on the direct victims but the nation as a whole."
Wiffin, who was abused from age 11 at the Epuni Boys' Home, told Morning Report the tragedy was avoidable if money and care had been put into helping young people rather than picking up the pieces later.
"Out of the institutions and homes comes the development of our gangs. It underpins our adult incarceration, it underpins our welfare dependency over many decades" - Keith Wiffin
The authorities need to be open and transparent about what's happening now and what's happened in the past, he said.
To get the scale of abuse that had occurred there had to have been very serious systemic flaws and failures in the system, Wiffin said.
"There needs to be some serious accountability for that.''
He said the figures were mind-boggling especially when considering those figures were for a period when the country's population was probably three to three and a half million people.
''An amazing percentage of the actual population.''
Minister for Public Service Chris Hipkins said the commission's interim findings were "harrowing".
Hipkins told Morning Report the government had set up the commission knowing the findings would detail some horrific stories.
"We have made a commitment we will allow the victims to see that report and to digest that before we make any further public comment on it."
Hipkins said he would be commenting on Wednesday afternoon.