The Work Permit is given to those who received a job offer in New Zealand by an employer with authorization to hire a immigrant and has not found suitabe native to work. The offer is established via contract. With the documents at hand, you should apply for a proper visa on New Zealand immigration. The visa will be granted according to the period described in the contract.
Variation - Seasonal Work: This visa is for whom will work in farms, doing fruit picking or vinery. The salary can range from NZ$9.00 to NZ$13.00 per hour or depending on the farmers.
International Student: This visa is for students willing to work while study. If you are studying for at least 6 months FULL TIME and have IELTS 5.0., your can apply for Variation which allows to work for 20 hours per week.