Air New Zealand has cancelled about 120 flights after the government announced there would be a delay to the phased reopening of international borders.

Previously, the government had hoped people arriving from Australia could self-isolate from mid-January, but that has now been pushed back by six weeks.

All existing quarantine-free flights from Australia to New Zealand between January 17 and February 28, 2022, will be cancelled and there will be a limited schedule of quarantine flights will be available to book.

The airline estimates about 27,000 customers will be affected by the cancellations, which are mostly for flights across the Tasman with only a small reduction in frequency on some long-haul flights.

Air New Zealand chief executive Greg Foran says this will be incredibly tough news for many.

"Our heart goes out to those who were counting down the days until they could reconnect with their family and friends.

"While this news is disappointing for the airline, we know these changes are put in place to keep Aotearoa safe.

"We are here for our customers, and as we have throughout the pandemic, we will continue to fly to get them home to Aotearoa as MIQ allocations allow."

Customers are asked to continue to check the airline's Travel Alerts page for further updates.

Customers who still wish to travel to New Zealand will need to secure a managed isolation spot before booking on a quarantine flight.

However, on Tuesday afternoon the government revealed that the latest release of MIQ rooms has been cancelled, with the next one due for January 6.

Air New Zealand will continue to operate a reduced schedule to Australia but will only be operating services out of Auckland.

Customers with bookings who no longer wish to travel can use the airline's online self-service tool to hold their fare in credit.

The airline has a policy in place for flights scheduled to depart before June 30, 2022, which means customers can change their flights without extra fees.

If customers have booked through a travel agent or third-party online agent, they will need to contact them directly to rebook or place their ticket into credit.

-RNZ.