Prime Minister Jacinda Ardern will not broaden the scope of the Government's inquiry in the abuse of children in state care to include religious institutes, community groups and sports clubs.

Groups of victims who have suffered abuse are calling for the Government to follow Australia's Royal Commission into Institutional Responses to Child Sexual Abuse, which looked at children in state care as well as religious institutes and sports, recreation, arts and culture, community and hobby groups.

The Australian inquiry found that most children sexually assaulted were abused in faith-based institutions.

The Care Leavers Australasia Network NZ has urged the New Zealand Government to include all forms of "out-of-home care", including homes run by churches, charities and foster care homes.

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But Ardern said the inquiry will start by focusing on abuse the state was involved in.

"This for us is about the role that the state played," she told Radio NZ's Summer Report this morning.

"We need to hold responsibility, we need to open ourselves up to inquiring into the harm we had direct responsibility for. We haven't even done that yet."

She said the inquiry would have a broad reach because the state had a broad reach.

"A child may have been in state care and then was placed in a particular environment, or had anything to do with the decision-making that led to that young person in particular being abused. The state's reach in that respect goes beyond state institutions.

"We might put out a starting point but an independent chair will go out and consult on those. That's the way we will include the voices of the many."

Ardern said she understood the concern from other people who have suffered abuse "beyond the state", and called on religious institutes to consider what they could do to look into allegations of abuse.

But she added that a church's internal inquiries wouldn't necessarily satisfy victims.

She said the inquiry would provide a better look at abuse than the Confidential Listening and Assistance Service, which concluded in 2015.

"[That] undertook a process of listening and reconciliation, but it wasn't open. It wasn't public. And there wasn't the release of those outcomes for everyone to see. It left victims feeling like we weren't learning any lessons."

The details of the inquiry are part of the Government's 100-day plan and will be announced before February 3.