The government is under pressure to follow Britain's lead and ban gay conversion therapies.
Theresa May's Conservative government has announced it wants to outlaw the controversial practice, as part of a 75-point plan to improve the lives of lesbian, gay, bisexual and trans people.
Gay conversion therapies have been outlawed in a number of other countries, but not in New Zealand.
Rainbow Youth executive director Frances Arns said gay conversion therapy was happening in New Zealand and it was more common than people might think.
"Surprisingly it's happening a lot in New Zealand.
"Recently someone told me that there's hundreds and hundreds of people in Auckland who have gone through a gay conversion therapy programme, so it's happening and it's really concerning."
Churches were typically involved in the conversion therapies, with pastors taking on the role of therapist, Ms Arns said.
But what the conversion therapy involved could vary.
"From my understanding, it's about helping you to change your sexuality, trying to suppress your attraction to people of the same gender," Ms Arns said.
It was something that could be particularly harmful for young people of faith who were struggling with their sexuality.
Ms Arns said the government should follow the lead of the UK and outlaw it.
"It's overdue and it's time for us to put a stop to a really outdated and harmful practice."
The Association of Counsellors and the Association of Social Workers were also backing those calls.
Blenheim counsellor Robyn McGill said she was surprised gay conversion therapies were happening here.
"My first reaction is just eye-rolling and thinking what part of the dark ages are we still in?"
Ms McGill said it can send a harmful message to young people.
"It's very dangerous when you aren't able to live your life in a congruent way, where you have to put on an act for this person and a different act for that person, and go to school and do this and at home do this.
"How do you make sense of all of that? How do you feel good or how do you like yourself, or how do you relate to the world or have a sense of belonging?"
A rainbow group in Rodney has set up a petition calling for the Government to ban gay conversion therapy. So far it has 2000 signatures.
Labour list MP Marja Lubeck has agreed to present the petition to parliament.
"There are so many people struggling with their sexuality and having these kinds of conversion therapies trying to change people from something that they know they are, does harm to these people," she said.
In a statement, the Human Rights Commission said there were no specific laws prohibiting conversion therapy in New Zealand.
It would support any moves by the government to consider ending this harmful practice, in light of Britain's decision.
Health Minister David Clark said he personally found the idea of gay conversion therapy "abhorrent".
While he had been advised that attempts to change someone's sexual orientation can cause them harm, the government has no intention to pursue a ban.