A backlog in applications for visitor visas has meant thousands of tourists have had to defer travel.
The Immigration New Zealand application portal currently carries a notice warning tourists from non-visa waiver countries not to book travel until their visas are approved.
"Due to the large number of applications received since 1 August processing times are longer than expected."
Immigration New Zealand general manager Richard Owen says immigration processing has been hit by an unexpected demand for travel.
"The volume of visitor visa applications we are receiving is much higher than we forecast," he said.
Between August 1 and October 4, New Zealand received more than 396,000 applications from international travellers wanting to visit, including NZeTAs from visa-waiver countries. Just over 90 per cent of these have been approved.
Owen says around 36,000 visitor visa applications are still awaiting a decision. However, immigration processing was having to prioritise the needs of visitors with the processing of other migrants seeking work or other visa classes.
"We are working incredibly hard to process all visa applications as quickly as possible and doing our best to balance the need to get visitors into the country with the need to get workers in – both of which we acknowledge are critical to New Zealand and our economy at the moment."
Immigration said it was "working towards" an application processing time of 20 working days.
On Friday, the National Party said that it was "very disappointing", publishing a statement that it was aware of more than 35,000 tourists from non-visa waiver countries who were still waiting for permission to travel.
National's tourism spokesperson Todd McClay said he had been contacted by tourism operators who felt let down by the slow processing times and feared they were losing international visitors to other markets.
"The New Zealand Government is telling potential high-spending visitors to not book travel until their visa has been approved. It is tantamount to telling potential tourists to go to Australia instead," McClay said.