Social Development Minister Anne Tolley has halted an experiment which would have seen 60,000 children monitored for two years to see if they were abused.

A plan to treat vulnerable newborns as "lab rats" by sitting back for two years to see if they were abused has been blocked by the Government.

The Ministry of Social Development proposed to include 60,000 children born this year in an "observational study" to test the accuracy of its new predictive risk modelling tool.

It attempts to predict abuse, welfare dependency and the likelihood of a child's downward spiral into crime on the path to adulthood so it can better target spending.

The Government gave the go-ahead to develop the model in 2012, as part of the Children's Action Plan. It had now begun testing it.

But documents show officials had sought ethical approval for one study which involved risk-rating a group of newborns and not intervening in high-risk cases, to check whether their predictions came true.

A furious Social Development Minister Anne Tolley said she could not fathom what her officials were thinking.

She has called a halt to the study.

The minister's handwritten notes on the documents instructed officials: "not on my watch, these are children not lab rats".

Anne Tolley annotated the report with comments.

Asked what justification MSD officials had for the trial, Tolley said she did not want to know.

"I was not impressed and I was not going to have a bar of it.

"I could not believe that they were actually even considering that. Whether it would have gotten through the ethics committee - I hoped it wouldn't."

The ethics proposal has now been withdrawn.

Tolley said those heading the project were "well-meaning" and "enthusiastic", but had not differentiated between an academic study and real life.

MSD deputy chief executive for organisational solutions Dorothy Adams said that while predictive modelling had merits it carried risks.

"It has been long acknowledged that while predictive modelling appeared promising based on preliminary research, it was at that time untried in the context of child maltreatment, carried ethical risks, and warranted careful, staged, development," she said.

"We were always going to carefully test and trial to understand effectiveness and this was simply one option."

Tolley also appeared to signal a major backdown on a proposed population-wide application of the model, saying it was "unlikely" to be used on children that had not already been notified to Child Youth and Family (CYF).

The tool is being tested in the CYF call-centre, with predictions being checked against known information.

"Where it goes from there is another big ethical question. Because God knows, do we really want people with clipboards knocking on people's doors and saying 'hello, I'm from the Government, I'm here to help because your children are going to end up in prison?' I just can't see that happening."

Its benefit was strengthening information available to social workers about children already involved in the system.

"Where we have a family that we're putting resources into, it does enable us to check and see what the wider family group might look like and make sure that we're getting to that family the whole group of agency assistance that we need."

Labour's children spokeswoman Jacinda Ardern said the observational study was "just wrong".

"If you have an indication that a child is in harm's way you should do something about it. Never would it be okay to not intervene in order to see whether or not your predictions were right," she said.

"It's shocking, but we've had problems with predictive risk modelling and the flaws that it presents since the moment it was floated.

"Now, we're just seeing that the minister has been presented with the stark reality of putting children, real children, through trials based on this model. I'm not surprised she's had the reaction she's had."