One of the world's leading authorities on child sex abuse in the Church says it will be a colossal waste of people's money if the government excludes churches from the Royal Commission into abuse in state care.
However, Prime Minister Jacinda Ardern said the inquiry would focus on those in state care because that's where the government has a duty of responsibility.
US Catholic cleric Father Tom Doyle first blew the whistle on the global scandal of clerical abuse in 1984, and has given expert evidence since, including at Australia's Royal Commission.
He has spoken out today in the wake of the Sydney Morning Herald and Newcastle Herald running stories of Australian abuse survivors urging the New Zealand government not to restrict this country's inquiry.
Mr Doyle said the evidence from all around the world was that the Roman Catholic Church has perpetrated, and covered up, more sexual abuse than any other institution.
He said if the government excluded faith-based and private institutions it would be an "abject failure".
Ms Ardern said five-year, $500-million Australian inquiry only dealt with sexual abuse.
"We've said anyone who was in the care of the state, whether we sent you to a boarding school or you went to a religious institution or you remained in state care, whether you were physically, sexually or emotionally abused, then we have a duty and responsibility to you and you will be covered by the inquiry - so in some ways we're broader [than Australia's Royal Commission]," she said.
"If anyone chooses to come forward and talk about their experience in an institution that's outside of the state, where the state hasn't had a role, then they are welcome to do that.
"But in terms of making a difference for those who have been victims who were in state care, that's where we have a duty of care and responsibility, that's where we can make sure that there is change."
The draft terms of New Zealand inquiry excludes cases that do not have state involvement - ruling out survivors of abuse while in Church care, or places like sports clubs - plus any abuse that occurred after 1999.
A three-month consultation period has just begun, which will include a visit to Australia by the commission's chair Sir Anand Satyanand in April.