Luckily, he didn't use a suppressor, otherwise it would be hard to tell there was a shooting for a while, there would be more people dead.The perception that semi-autos are banned in Australia is completely false and spread by the media. They may be heavily restricted, but not unobtainable, I have an A15 and AR10.
New Zealand's gun laws are fairly relaxed compared to Australia. Most New Zealand gunshops stock semi-autos and suppressor's available on a hunting license.
The fall out of this shooting will no doubt trigger the anti-gunners and leftist politicians in both countries. More than likely they'll succeed in restricting firearms further.
I guess the licensing for semi-auto and suppressor need to be more strict and/or with a psychological test and background check every few years if you own or intend to buy in New Zealand now.