INZ figures show it has 179 fewer workers than before the pandemic.
Since December, it has received 91,000 applications for 181,000 people to get residence under the government's fast-track scheme. And next month, the twice-delayed Accredited Employer Work Visa (AEWV) will begin to replace six work permit categories, with the first visas due in July.
Immigration's general manager of border and visa operations, Nicola Hogg, said it was recruiting for more New Zealand staff and has opened a second office in Christchurch after closing three overseas offices last year.
"INZ is constantly reviewing our capacity and capability to ensure we have the right level of resources to process anticipated incoming visa volumes.
"The new staff we hire are trained across a number of different visa categories as we are always training and moving staff between different visa categories, depending on incoming visa volumes. We will continue to do this as we process 2021 Resident Visas, while also opening offshore applications in line with the government's Reconnecting New Zealand plan.
"INZ currently has 658 Immigration officers processing and making decisions on visa applications. In February 2020 when the borders closed due to Covid-19, INZ had 837 Immigration Officers processing visa applications in Auckland, Christchurch, Porirua, Hamilton, Palmerston North and in overseas offices."
Some migrants worry about how quickly they may get visas approved once they are able to apply in October, especially split families wanting to reunite before Christmas.
For others with expiring visas, October will be too late.
Figures released to the Green party immigration spokesperson Ricardo Menendez March show an average of 20,000 visas expire each month from now till October.
Migrant Jagdeep Singh, who had a post-study work visa but was in India when the border closed, said more than 80 percent of visas had already expired.
"It's discrimination with us," he said. "We want to extend our visa or get a replacement visa same as in Australia. Our future and life has been totally destroyed, it's against humanity. Nobody has listened to us."