Director of Public Health Caroline McElnay says officials don't know how long the Omicron variant of COVID-19 can be kept out of the community.
On Thursday, New Zealand reported 43 COVID-19 infections at the border - more than double the community case tally. The Ministry of Health has said the border infections are likely Omicron.
There are currently no known cases of Omicron in the community, with all of New Zealand's locally acquired cases still stemming from the Delta variant outbreak that unfolded in August.
"While whole-genome sequencing of these cases is expected soon, the likelihood is that Omicron will continue to be the most prevalent variant at our borders," the Ministry of Health said of Thursday's managed isolation cases.
Overall, Omicron continues to have a significant impact globally, the ministry said.
"It is not unexpected to see an increase of Omicron cases at the border."
On Friday, Dr McElnay said the ministry was working to get more rapid antigen COVID-19 tests into New Zealand in preparation for Omicron.
Asked about the global supply issues for rapid tests, including in Australia where Omicron cases have exploded in recent weeks, Dr McElnay told RNZ the ministry was working to get stocks into New Zealand.
"I'm aware that there is a worldwide shortage of rapid antigen tests - that is one of those supply issues that we need to make sure we've got sufficient [stock] in the country.
"At the moment, what we are doing is trying to slow down the arrival of Omicron into the country, that is where our efforts are focused - at our border. We don't know how long that will last so we're working as fast as we can to make sure that we are prepared.
"The rapid antigen tests are only one part of the strategy… the testing is part of an overall strategy to minimise the impact on our community at large and on our health system as well," Dr McElnay told RNZ.
There were 19 new Delta cases in New Zealand on Thursday - nine in Bay of Plenty, five in Auckland and three in Waikato.