Covid-19 modelling experts warn the highly-transmissible Omicron variant poses a serious risk to a largely unrestricted summer.
Thirteen cases of the variant have now been picked up in managed isolation and quarantine.
The first one was on Thursday, then another on Friday, then three more were announced, then four more, then yesterday five further cases of Omicron were notified by the Ministry of Health. The cases are in MIQ in Auckland and Christchurch.
More cases would keep arriving at the border, increasing the chance one would leak out into the community, Te Pūnaha Matatini complex systems researcher Dr Dion O'Neale said.
"At the moment most of those [MIQ] infections will be Omicron from now on, purely because Omicron is most of the cases in countries that people are coming back to New Zealand from.
"At some point it does become a matter of time until that gets out into the community," Dr O'Neale said.
With Omicron, O'Neale said, some environments clearly posed a high risk, such as nightclubs and concerts. But even environments like restaurants and cafes could be the site of dozens of infections if a positive case attended.
"It's the case of having lots of small events where people might be infecting dozens of people at a time. That's a way that you really quickly get things out of control. Orange, as a traffic light level as part of the Covid Protection Framework, isn't really fit for purpose if we have Omicron in the community."
He said an outbreak here would probably mirror what's happened in New South Wales.
Two weeks ago the Australian state had around 200 cases a day, while on Sunday it recorded 2558. The state's health authorities believe most of the cases are Omicron.
Even a single case here could jeopardise some of our hard-fought freedoms, Covid modeller Michael Plank said. It would depend if the case had a clear link to the border or had been in the community.
"If we did have a case in the community, we'd need a really intensive contact tracing operation around it, and there may be a case for additional restrictions on top of that."
If the variant became established, Plank would expect it would spread "extremely quickly", as even fully vaccinated people were not as protected as with Delta.
"The ability of Omicron to infect people who have had both doses of the vaccine is significantly higher than for Delta".
There have been over 10,000 Delta cases in this outbreak, of which Māori make up nearly half.
Dr Sue Crengle of Te Rōpū Whakakaupapa Urutā, the National Māori Pandemic group, said Omicron posed another risk and community cases should trigger action.
"I think we should use a heightened level of restrictions, especially if it's in regions where there are high numbers of Māori and there are lower vaccination rates."
Auckland Business Chamber chief executive Michael Barnett said any stronger restrictions would not be tolerated by businesses or even, in his view, regular Aucklanders.
"I don't think Auckland would be prepared to take any further constraints, constrictions. They've been in lockdown for what, 115, 120 days, they're tired of it," Barnett said.
"I think government should be making it abundantly clear what are the conditions under which they would impose any constraints."
The Ministry of Health said it and the MIQ teams had been "carefully planning" for Omicron cases at the border.
All passengers on flights with Omicron cases must spend all 10 days at a managed isolation facility, rather than seven in MIQ and three in home isolation like other arrivals.
Chair of the Strategic Covid-19 Public Health Advisory Group, Professor Sir David Skegg, says although New Zealand has one of the most robust MIQ systems in the world, no system can be fail-safe with a variant like Omicron.
"It is urgent now for the government to just review our MIQ procedures and see where things can be tightened to reduce even further the risk that Omicron spills out into the community," Skegg said.
Skegg said it was possible but unlikely that Omicron is already in the community.
He said in order to keep Omicron out of the community the government should require international returnees to provide PCR test results prior to arrival rather than the less accurate rapid-antigen tests.
"If you're early in the infection it doesn't matter what test you do it probably won't show up as positive, you can be infected and for several days you'll return a negative test... that's especially true of rapid-antigen tests which aren't nearly as good as PCR tests."
However, he said it was not a watertight strategy as even PCR tests can fail to identify an infected person who is incubating the virus.
Skegg said after the government reduced the mandatory MIQ stay time to 7 days they should now consider resetting it back to a 10 period.
Although the government would likely face scrutiny for re-tightening restrictions, he said these decisions need to be made on a public health basis.