A sole immigration agent in China is believed to be responsible for 279 fraudulent student visas issued over the past year.
Immigration NZ is still searching for 246 students in New Zealand as a result of fraudulent visa applications processed in Beijing, including 74 illegal overstayers.
All may be liable for deportation if caught.
The head of Immigration NZ, Steve Stuart, is currently in China visiting the department's offices in Beijing and Shanghai, Radio New Zealand reports.
He said investigators had found the fraudulent documents - including fake qualifications and falsified bank statements - and it was believed all of them had been submitted by one agent at Immigration NZ's Beijing office.
The man has refused to be interviewed, and is set to meet this week with Chinese authorities, who will decide what action to take.
Mr Stuart said the students told investigators in New Zealand they did not know fraudulent documents had been used to support their visa applications.
A week ago, Immigration NZ said five students were in custody awaiting deportation, while 31 others had been tracked down and also faced deportation.
Some of the students were believed to have been working at a Blenheim vineyard, despite not being entitled to work.
Their employer could face charges.
All of the students were enrolled at 20 education providers in the Auckland area, Government ministers said.
NZN