Kiwis are being urged to use the Government's contact tracing app and get tested for COVID-19 as concerns about community transmission grow.
New Zealand hasn't had a locally transmitted case of unknown origin for more than three months, but with cases detected at borders overseas now being linked back here, there are fears undetected cases could spark a new outbreak and force the country back into lockdown.
Testing and tracing efforts are underway in regions around the country visited by a person who's tested positive in South Korea. Another case has emerged in a person who travelled to Sydney from Auckland.
Leading microbiologist Siouxsie Wiles says the authorities will be frantically trying to find out how they contracted the virus, and when.
"They might have had the virus before, it might be a false positive, or they could get it en route," Dr Wiles told Newshub on Sunday.
"What's really important though is it could be a sign they got infected in New Zealand, so we have to absolutely rule that out. The way we do that is by ensuring that we keep up the numbers of tests we do out in the community. If somebody has symptoms, they really must call Healthline or get in touch with their GP and ask to be tested."
The number of tests being carried out has fallen well below the targets. Few people are also using the contact tracing app, despite it having more than 600,000 downloads.
"It is only registering 12,000 scans per day," said National health spokesperson Shane Reti. "This means less than 0.25 percent of New Zealanders are using it."
Fewer possibly, with Kiwis able to scan it more than once a day.
"With more than 200,000 New Zealanders on unemployment benefits as a result of lockdown, we cannot afford for our tracing systems to not be up to standard," said Dr Reti.
Dr Wiles said if Kiwis don't, they had better start "mentally preparing" for further measures to be taken to stop the virus, which has killed more than 680,000 people already.
"Starting to think about, for example, one thing that's starting to become really prominent around the world is the use of masks. You don't have to use the surgical masks - there are people who are making homemade masks, start to think about that. You want to get a supply of those.
"Download the Ministry of Health contact tracing app, use it. They've now got a new functionality where if a place doesn't have a QR code you can add your details manually. Start doing that, because we need to know where we've been if we end up being a contact for somebody."
As for whether the new cases overseas linked to New Zealand caught the virus here, Dr Wiles says there are several possibilities.
"They might have had the virus before, it might be a false positive, or they could get it on route. What's really important though is it could be a sign they got infected in New Zealand, so we have to absolutely rule that out. The way we do that is by ensuring that we keep up the numbers of tests we do out in the community. If somebody has symptoms, they really must call Healthline or get in touch with their GP and ask to be tested.
"People can test positive for quite some time after they've had an infection. It depends when that was. If it was before we went into lockdown... it wouldn't have transmitted anywhere else because we went into lockdown. It would have been stopped then."
People also can transmit the virus for a few days before they show symptoms or test positive, hence the warnings.
"We're becoming quite complacent here in New Zealand," said Dr Wiles. "Obviously we're at alert level 1, so we're doing all of the kinds of things that if the virus does come back, are going to make it much easier to transmit. We just need to be really mindful that we keep washing our hands, if you are unwell call your GP and stay at home - don't go to work if you're unwell."