These are pages with a very good description of causes and symptoms of hoarding: About Hoarding. Hoarding Disorder.
A simple guide to helping a hoarder yourself – Health Navigator New Zealand – How To Help A Hoarder
Professional help
Psychology Today NZ – Hoarding Disorder to find therapists who can help with hoarding behaviours, click the Find Counselling in the blue banner at the top and click on your city. Click the All Filters button. Click the Show More Specialities link. Click Hoarding.
If you need caring support for an elder hoarder – https://www.ageconcern.org.nz/
Support and Information
Auckland Libraries has several books on the subject of understanding and managing hoarding behaviours: Books about hoarding behaviours that you can borrow.
The Taranaki DHB have written an interesting document a few years ago: Hoarding And Squalor Guidelines
The Southern DHB wrote something very similar: Good Living Conditions Southern
Community & Public Health Canterbury Enabling Spaces – Supporting older people who hoard in Canterbury
This UK public Facebook group shares useful information and articles for people with hoarding behaviours, professionals who help them and family and friends. https://www.facebook.com/HoardingDisordersUK/
How to Help A Hoarder written by a respected resource on ADHD and Executive Functioning.