Reference: http://www.landtransport.govt.nz/factsheets/43.html
Is it a moped or a motorcycle?
There are slightly different definitions of a moped, depending on the context:
For vehicle registration and licensing: a moped has a power output of 2 KW or under and a maximum design speed of 50 km/h or under. A vehicle with a power output over 2 KW or a maximum design speed over 50 km/h is a motorcycle. It is illegal to register a motorcycle as a moped.
For vehicle importation inspections: a vehicle with an engine over 50 cc or a speed greater than 50 km/h must meet the technical requirements for a motorcycle.
For in-service inspections: a vehicle with an engine over 50 cc or a speed greater than 50 km/h or a power output greater than 2 KW needs to have a warrant of fitness and must meet the technical requirements for a motorcycle.
If your vehicle qualifies as a moped, it can be ridden with any valid drivers license (not requiring a Class 6 / Motorcycle license). You must wear an approved helmet.
For more info refer above link (found by searching for 'moped' at landtransport.govt.nz).
Cheers.