Health authorities revised their RAT order last week, buying another six million rapid tests.
New Zealand has reported just three community cases of the Omicron COVID-19 variant to date, including a British DJ who left his self-isolation early to party in Auckland.
The other two cases were an Air New Zealand crew member and their household contact, with no further spread across the community.
However, with dozens of cases found in international arrivals on a daily basis, it appears to be just a matter of time before it leaks from the border regime.
COVID-19 modeller Michael Plank, of the University of Canterbury, said mounting cases in the quarantine system - known as MIQ - added risk.
"For the bulk of last year we were seeing two or three cases a day on average and we're now seeing cases in the 20s or 30s coming into MIQ per day," he said.
"From 1 Jun to 1 Dec (2021) we averaged about 2.6 MIQ cases a day and had one border-related outbreak.Â
"MIQ cases are now up by a factor of over 10. If that continues we might expect the next outbreak to occur in 18 days rather than 180 days."
New Zealand has held onto the more rigorous PCR testing regime through the pandemic.
It is now using RATs in government healthcare settings for staff and visitors, as well as in the police force and prisons.
Unvaccinated Kiwis leaving Auckland - the centre of the Delta outbreak - this summer need to get a RAT at a pharmacy if they are going on a road trip, or through Air New Zealand or on the Cook Strait ferries if travelling by air or sea.
A number of businesses are also using RATs for their staff.
In the event of an outbreak, RATs will be used more broadly - prompting the Ministry of Health to stock up.
"The Ministry of Health has nearly three million rapid antigen tests currently ... we have recently revised our order in light of Omicron and what is occurring in other jurisdictions and have increased our forward order to six million rapid antigen tests," a spokesman told AAP.
Despite a global shortage of the tests, New Zealand expects to receive supplies "in stages over the coming days and few weeks".
Government ministers are on leave, but a spokeswoman for deputy PM Grant Robertson said bureaucrats were watching ballooning case numbers in Australia carefully.
"Ministry of Health officials are in constant communication with their counterparts in Australia," she said.
"As you would expect, anything we learn from Australia informs our planning and preparedness for Omicron cases in the community, as the pandemic continues to evolve."
The other key part of New Zealand's Omicron preparedness is its vaccination program.
New Zealand has strong vaccine coverage - 92 per cent of Kiwis aged 12 and over are fully vaccinated - and has shortened the wait time for booster shots from six months to four.
That will mean more than 80 per cent of jabbed Kiwis are eligible for boosters by the end of February.
University of Melbourne epidemiologist Tony Blakely said New Zealand should "boost like crazy" in the next six weeks.
"Try and get at least two-thirds of the over 60 population boosted ... before Omicron comes in, and get the public ready," he told Radio NZ.
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