Megan Woods, the minister in charge of the Government's managed isolation facilities, insists "space isn't going to run out" despite asking Air New Zealand to freeze ticket sales for three weeks.
The Government has announced that Air New Zealand will "put a temporary hold on new bookings" to ease the pressure on the facilities which are currently housing nearly 6000 returnees.
Dr Woods said on Tuesday the Government has been monitoring the incoming flows and matching it with the current capacity at the 28 facilities spread across Auckland, Hamilton, Rotorua, Wellington and Christchurch.
"Over the weekend, we had greater numbers than anticipated arrive. For example, on Saturday 98 transit passengers out of Hong Kong arrived that were not scheduled for. It became very apparent to us that we needed to take some demand-side measures as well supply-side."
Dr Woods said Air New Zealand agreed to restrict the number of tickets being sold so the Government could have a clear understanding of how many people it needed to facilitate.
"Since June 17, when Air Commodore Webb and I took responsibility for this task, we've brought on over 2000 places spread over 10 facilities - so we have been scaling up," she said. "But we cannot just continue to let this be a purely demand-driven system.
"For those people who were looking to do a little less planning ahead of it, there's not always a guaranteed air ticket for every destination that you want to go to. I think all of us have probably encountered that. There will simply be a three week wait."
Dr Woods said any New Zealander who has already booked a ticket over the next three weeks will be able to complete their journey, but new bookings are not being taken for three weeks.
"We're talking about a very short-term measure here to ensure we are protecting the gains that New Zealand has made and something that we all made a huge amount of sacrifice for. We have to do this in a measured way."
Dr Woods said Air New Zealand is currently at around 30 percent loadings and the Government has asked the airline to keep it at that capacity for the next three weeks.
"Space isn't going to run out. We have data from the airlines around who is coming back. This is exactly why we've taken this measure so that we can ensure that our managed isolation facilities continue to be a strong line of defense at our borders."
The border is currently only open to returning New Zealanders and residents and each returnee is required to undergo 14 days in managed isolation and must test negative for COVID-19 before being allowed to leave.
But since alert level 1 came into force in June there has seen a huge influx of returnees.
More than 26,500 people have been through managed isolation and quarantine since March 26, but 28 percent of them - 7682 - have gone through since June 17.
Foreign Affairs Minister Winston Peters stressed back in March for Kiwis to come home and Dr Woods said the Government is doing all it can to accommodate them.
"We've been doing everything we can to facilitate what needs to be done so New Zealanders can return home. But we also have to be mindful that we're putting in place safe and secure managed isolation and quarantine facilities."
What about other airlines?
Air New Zealand makes up about 80 percent of the inflow and Dr Woods said it was "absolutely critical" that the airline worked with the Government or it "wouldn't see the shift in numbers we need".
She said the Government has been talking to the other airlines that are currently flying into New Zealand and they are "also going to do some of the measures" to ensure they don't take advantage of Air New Zealand's reduced capacity.
"We didn't want Air New Zealand doing this just to have other airlines pick up that volume anyway so those conversations have been happening with other airlines."
ACT leader David Seymour said restricting New Zealanders from coming home for three weeks reflects the "level of its incompetence" at the border.
"New Zealanders will be asking whether it is legal to restrict the right of citizens to return home, or whether Air New Zealand has been pressured into restricting flights so that the Government can avoid any legal responsibility."
Dr Woods said the Government has been seeking legal advice "all the way through".
"It is absolutely every New Zealanders' right to come home but it is also every New Zealanders' right to feel that the Government is managing isolation in a way that protects them."