This isn't necessarily a knee-jerk reaction.
In 1996, Australia had it's anti gun legislation written up years ahead of Port Arthur shooting that allowed the parliament to ram it through with no opposition.
New Zealand would have had this legislation prepared well ahead of time in order to trot it out in response to an appropriate tragedy.
This legislation did not come about in a vacuum. They are using all the same buzz words used by anti gun groups globally. High capacity, military-style, assault rifles.
Interesting side note, this isn't legislation in the common meaning of the term.
NZ Parliament didn't vote on this, it is an edict from their Cabinet.