Use the Town/City locality type for New Zealand.

Source: https://www.nzpost.co.nz/personal/sending-within-nz/how-to-address-mail/standards-guides

Author: bojanz

formats.go

@@ -1159,6 +1159,7 @@ var formats = map[string]Format{
 	"NZ": {
 		Layout:            "%1\n%2\n%3\n%S\n%L %P",
 		Required:          []Field{FieldLine1, FieldLocality, FieldPostalCode},
+		LocalityType:      LocalityTypeTownCity,
 		PostalCodePattern: `\d{4}`,
 	},
 	"OM": {