This index came to my attention today in the New Zealand Society of Genealogists magazine. The ONI was created from documents held by the Hocken Library in Dunedin. The index is hosted by the University of Otago.
If you have ancestors in this area, this database will be 'a must look into' resource. I have only one family which lived in the South Island and they aren't mentioned but you may be lucky. The index will point you to the original documents which may contain more information.