Vehicles are registered before you buy them from the dealership and the plates stay with them for the life of the car. They don't do the 30-60 day temp tags like in the US. And since you can't just drive the car from another state/country (they only have one plate for the whole country instead of state-based tags), you will never see anything other than NZ plates.
Because I didn't buy my car locally, it needs to be inspected to ensure it meets local laws before it can be registered. So technically, I have to have it towed to the inspection facility and once it passes then I'll be able to buy plates for it. Then, cars need to have a Warrant of Fitness inspection every 2 years (longer if purchased new) in order to renew plates. Additionally, NZ laws require all cars to be right-hand drive, so I had to apply for an exemption permit to avoid having to convert it. They only allocate 500 permits per year and they were out by the time I got the paperwork done last year, so I had to reapply at the beginning of 2017.