Secretive, closed faiths - including Gloriavale, Exclusive Brethren, and Jehovah's Witnesses - will be formally investigated by the Royal Commission into Abuse in Care.
The Commission's Anglican investigation has also been expanded to include the Methodist, Presbyterian, and Salvation Army faiths.
A spokesperson for the Commission said expanding the investigation was to recognise the large numbers of people from each organisation willing to pass on information.
"The scope is being formally extended to recognise increased numbers of survivors from these faiths and their institutions - including schools and care homes - who have disclosed abuse to the Royal Commission."
Newshub understands up to 60 people who left Gloriavale have engaged with the Commission's lawyers, completing face-to-face interviews or providing written evidence.
The Gloriavale Leavers' Trust manager Liz Gregory said she's very pleased with the development and the way the Commission had responded to its concerns over the past two years.
"The Commission got lawyers involved to interview leavers. They worked with us to bypass some of the roadblocks we faced."
The fresh investigation will consider evidence of abuse, which includes physical, sexual, emotional, or psychological abuse and neglect.
It will consider the impacts of such abuse, any structural, systemic, or practical factors which contributed to abuse, and consider domestic and international law, including human rights law.
There won't be public hearings, but findings of the expanded investigation will be released before June next year.
The Commission is encouraging any other survivors who have not already spoken to them to get in touch.
"Survivors who want to share experiences about abuse by any of these faiths are encouraged to call us confidentially on 0800 222 727 or register on our website and we will phone you."