Your NZ income tax obligations will depend on your individual circumstances, and we strongly recommend you obtain independent tax advice from a professional accountant regarding your personal tax situation.
If you are contracted directly to a hospital or general practice you may be engaged either as an employee or an independent contractor, depending on the terms of your agreement. If you are working as a locum and contracted to NZMedics you will be engaged as an independent contractor.
Things you will need to consider are:
Income tax for 'Tax Residents'
The New Zealand tax department is called the Inland Revenue Department (IRD) and all information, forms and enquiries can be found online. There is a dedicated team at IRD that deals with Non-Resident Contractors which you can contact to apply for tax exemption.