The NZ bus system is city/regional town to city/regional town.
https://www.intercity.co.nz/ and the like.
For tourist type activities it then steers you to guided bus tours designed for tourists. 1000's do this, including many from Asia. As above, Queenstown area caters to that market as does the Rotorua area. It will take a lot more time than if you had a car.
Samples:--
https://www.newzealand.com/au/buscoach-transport/
https://www.newzealand.com/au/trips-...ies/8-14-days/
For something a little different you could take the ferry Wellington to Picton (a good ride) and connect to the Coastal Pacific train to Christchurch. The train to CHC restarted a few days ago, after a the Kiakoura earthquake damaged the south road/rail link
https://www.greatjourneysofnz.co.nz/