NZLII is a valuable source of full-text case law. Scope varies but includes Supreme Court, Court of Appeal and High Court decisions from at least 2005; plus a lot of decisions from tribunals and authorities.
There are 3 major publishing houses. Knowing who publishes what will speed up your search.
Butterworths = LexisNexis. They publish the official reports: the New Zealand Law Reports.
Brookers = Westlaw = Thomson Reuters
CCH = Intelliconnect = Wolters Kluwer
This page is designed to help you find and use NZ case law.
If you have a full citation to a reported case, use the Cardiff Index to Legal Abbreviations to decode the citation (if you need to), then search the library catalogue for the title of the report series; then find the full text - which may be print and/or online.
For just about everything else, start with index databases, then move on to full-text sources.
Two exceptions to that general rule:
Reported cases are published by commercial publishers. These cases are selected because of their legal significance, typically because they state or develop a point of law, so they are a good source of legal authority.
The New Zealand Law Reports (NZLR) is New Zealand's official law report series.
Other New Zealand report series deal with cases on a particular area of law.
An unreported case is the court document. The case may subsequently be reported, if it is significant; or it may remain unreported, in which case it is more likely to cite the authorities you need rather than to be an authoritative case.
Indexes and case citators