If you are in New Zealand for more than 183 days, you are regarded as a New Zealand tax resident and income tax will be deducted from your salary. If you are working as an independent contractor and in New Zealand for more than 183 days you will be required to pay tax on your earnings.
Non-residents are only taxed on New Zealand sourced income whereas permanent residents are taxed on worldwide income.
Current tax rates for individuals can be found on the Inland Revenue website here.
The tax year is 1 April to 31 March and tax returns must be filed by 7 July for the preceding tax year.
New Zealand tax residence guide can be viewed here.