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.
The country's independent association for tourism and leisure, Tourism Industry Aotearoa said it was aware of the processing delays for visitors.
"We absolutely want all our visitors to be able to enter the country as quickly and easily as possible," a TIA spokesperson said.
However, they saw that many factors outside New Zealand's control were still restricting numbers from non-visa waiver countries.
One of the main markets requiring visitor visas - China - was still enforcing strict travel restrictions, depressing demand for overseas tourism.
In general, they said the resumption of the NZeTA and Working Holiday visas in April had been a huge help for New Zealand's tourism businesses.
Immigration NZ said processing times for NZeTAs for countries with a visa waiver agreement was not affected, taking a maximum of 72 hours to process.
It was its long-standing advice for tourists not to book any travel before visas are finalised, Owen said.
"We advise people to wait until they have received an outcome so that they are not at risk of being unable to use their travel bookings and out of pocket."