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:
Tax Exemption
Income tax for 'Tax Residents'
GST
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.