In early 2017, about 150 Indian students had to leave New Zealand after it was discovered their visa supporting documents were fraudulent.

The number of Indian students applying for visas has plummeted, new data from Immigration New Zealand shows.

The government agency's staff in India considered just 9429 study visa applications in 2017, down from 16,380 in 2016 and 25,977 in 2015.

Of the 9429 applications, 6429 were approved and 3004 – just under a third – were declined.

That is down from both 2016 and 2015, when more than half of all student visa applications lodged in India were declined.

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The data set captured all fee paying and scholarship student visa applicants who were outside New Zealand at the time of their application.

The downtown comes after about 150 Indian students were threatened with deportation after it was discovered their visa documents were fraudulent.

The students had each paid about $20,000 to arrange for the visas, only to discover after arriving in New Zealand that their supporting documents had been forged by agents in India.

Most left the country voluntarily in early 2017, but later said they had struggled to adjust to life back in India.

Some said they had been denied jobs and faced stigma because of their ordeal.

Immigration New Zealand spokesman Marc Piercey said student visa approval rates for India had "traditionally been lower than elsewhere" due to market complexities and a "high incidence" of fraud.

"The lower number of applications and higher approval rates in the past few months indicates that the overall quality of applicants has increased and the majority of providers are heeding advice about the need for higher quality applications."

Students from countries with a visa decline rate of more than 20 per cent, like India, must show greater proficiency in English than those from countries with lower decline rates in order to be granted a study visa.

That proficiency is assessed by the New Zealand Qualifications Authority before an international student can be enrolled at an institution.

Of all the countries, China was the one with the most offshore student visa applications.

Immigration New Zealand staff in China processed 7869 applications, of which 7327 were approved and 542 declined.

The United States saw the third-most applications lodged, after India, with 2543. Of those, only 36 were declined.

Other countries where high numbers of student visas were granted were Japan (2215, out of 2229 applications), Thailand (1578, out of 1690), South Korea (1548, out of 1591), Brazil (1510, out of 1660) and Germany (1324 out of 1330).