An expert says health officials need to encourage mass testing in Northland after confirmation of a community case in the region.
The Ministry of Health confirmed they were investigating a positive test result in a person who had departed from a MIQ facility.
University of Auckland Professor Des Gorman told Newstalk ZB the news was concerning.
"Hopefully it will turn out to be a situation which can be quickly contained," Gorman said.
"But it is a worry in the context of new strains coming in from the UK, the US and South Africa which are more infectious.
"Any breaches of the border have the potential to lead to quite significant community transmission."
Arrivals get tested on about the 12th day of the two week-stay in MIQ and are able to leave if the test is negative.
It is possible the woman picked it up in the facility after her final test and was incubating it when she left.
Covid 19 Response Minister Chris Hipkins and Director General of Health Ashley Bloomfield gave more details at a press conference at the Beehive at 4pm today.
If positives cases started turning up and there was no clear link to somebody in quarantine, that would lead to a lockdown, Gorman said.
He said officials would be "scrambling" to test all contacts.
"What they need to do now in Northland is to encourage widespread community testing, just to make sure there aren't any other cases.
"What's required now is not only to test the people who have been in direct contact like family members and so on, but also to start encouraging people to turn up and be tested en masse.
"So that in fact there can be some reassurance that there aren't other cases in the community."
Covid-19 modeller Professor Michael Plank said it was possible the virus may have been passed from an infected person to another in a MIQ facility.
"One of the risks we've always been aware of is someone arrives with the virus, but then they pass it on to someone else in quarantine, perhaps near the end of their stay," said Plank, of the University of Canterbury and Te Punaha Matatini.
"That's one possible way the virus can leak out. I'm not saying that's what happened in this case, but it's a possibility, because it would be unlikely for someone to be incubating the virus for that length of time."
Plank said contact tracers would be racing to find all of the close contacts that may have been exposed - and any other linked cases would hopefully be revealed over the next few days.
"The best case scenario is that they haven't gone to any major parties or gatherings.
"But we won't know that until that information comes out and this will give us a better idea about what the level of risk actually is."
The last case of community transmission in New Zealand was on November 18.
At today's 1pm Covid update, the Ministry of Health announced there had been eight new Covid cases in managed isolation since Friday.
The cases came from South Africa (2), the UK, United Arab Emirates, the US (2), Ethiopia and India. Four travelled via UAE and Malaysia.