I once boarded a plane in Christchurch without going through security and changed planes in Auckland without going through security, then flew right into LAX. I could have had an M-16 with me, and nobody would have ever known. I hope that's changed.
We now have security checks for all transfer passengers and departing passengers on both international and trunk domestic flights.
Still, security is a bit lax than when compared with many other airports overseas: I travelled on AKL-PPT (papeete/Tahiti) - LAX-DFW-DTW two years ago. My shoe sole was a bit damaged due to wear over the years and it didn't activate the metal detector in Auckland but did at Papeete and LAX. This tells you how laxed security here really is, and the security screenings are done by a government department in NZ as well (Aviation Security Service).