Immigration NZ is taking action to stop students coming to New Zealand from Vietnam on fraudulent paperwork.
Immigration New Zealand assistant general manager Jeannie Melville said a "significant" amount of fraud was detected by its Mumbai office earlier this year.
"We have found 47 cases of this specific financial fraud in the Vietnamese market and we are taking appropriate action including cancelling visas and preventing people travelling to New Zealand," Ms Melville said.
A number of education agents were implicated in the fraud, which involved students across all sectors of the New Zealand education system, she said.
Consolidation of its visa processing programme from a geographical model to a product-based model and shifting the service to its Mumbai office picked up the problem.
Ms Melville said the Mumbai office had experienced staff who were well versed in detecting fraud.
Immigration New Zealand and Education New Zealand have agreed to an industry and agent engagement programme to grow high-quality student enrolments from the Vietnam market.
Lisa Futschek of Education New Zealand's international division said New Zealand had an important and growing education relationship with Vietnam.
She said there had been a 55 per cent increase in valid student visas from Vietnamese nationals from June 2013, when 1401 visas were issued, to June 2019, when the number grew to 2174.
Growth was particularly strong in the secondary school and university sectors, Ms Futschek said.
Ms Melville said the immigration system was based on honest and truthful self-declaration from applicants.
"If this obligation of honesty is breached, we will have a zero tolerance to such behaviour and will take decisive action."
Processing times for visa applications have been longer due to higher numbers of applications and fraud concerns.
"Some quality applicants with legitimate intentions are unfortunately getting caught up in the large volumes of low quality applications that require high levels of verification," Ms Melville said.