You need to complete an IR595 form from the Inland Revenue Department. You must be personally in New Zealand to apply for an IRD number (you cannot apply from overseas).
You are required to provide originals of two identification documents (such as a birth certificate or driver's licence) plus a legible photocopy of these documents.
Take the completed application form and supporting documents to an Inland Revenue-appointed verifier. These are:
They will verify your supporting documentation and return the originals to you, then forward your application form and photocopies to Inland Revenue.
Inland Revenue will send you your IRD number within 8 to 10 working days. It is sent to your residential address, or, if it is urgent, Inland Revenue can advise you of the number by phone.