A professor of public health has reassured New Zealanders they should go about their "business as usual" after the first confirmed case of coronavirus, and that the risk of contraction is low.

Last night and this morning shoppers descended on supermarkets to stock up after news of the first confirmed case of coronavirus on New Zealand soil.

A person in their 60s is in isolation at Auckland City Hospital after returning from Iran via Bali.

But University of Otago professor of public health Michael Baker said there was no evidence of silent transmission, which means others have been infected but it has not yet shown up.

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If there was silent transmission, "you'd have seen some evidence by now", Baker said.

"Australia and NZ have been fortunate and planned very carefully for this."

How the case was dealt with was actually "a really nice example of how the [Kiwi health] system is responding" to the world health emergency.

A monitor displays an image of a thermal scanner as passengers pass through a quarantine station at Narita Airport in Narita, Chiba Prefecture, Japan. Photo / Bloomberg
A monitor displays an image of a thermal scanner as passengers pass through a quarantine station at Narita Airport in Narita, Chiba Prefecture, Japan. Photo / Bloomberg

The infectious disease expert said even people who were on the same Emirates EK450 flight as the infected person should not be overly worried.

The flight arrived from Tehran, via Bali, into Auckland on Wednesday.

"They shouldn't be particularly concerned. It doesn't get transmitted completely throughout the airplane environment. It depends on what symptoms were on the flight," Baker said.

He added that probably the only ones who needed to be worried were those near the confirmed case on the plane.

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Baker said New Zealand was "still a long way off social distancing measures" of its citizens, after the first confirmed case.

But he ended on a more concerning note.

"Eventually we will see widespread transmission in NZ," Baker said, qualifying the important thing was how it was managed by health authorities.

In a statement, the Ministry of Health said the person in their 60s was alerted to health authorities after their family became concerned about their condition and called Healthline.

"They were advised to seek medical attention and attended Auckland City Hospital emergency department that same day. All were wearing masks on arrival. As a result of the individual's symptoms and travel history they were admitted and tested."

The results of the test were confirmed at 4.15pm yesterday and makes New Zealand the 48th country to have a confirmed case of the virus.

The person is in a stable condition.

Professor Michael Baker (left) and Professor Nick Wilson, of the Department of Public Health at the University of Otago, Wellington. Photo / Supplied
Professor Michael Baker (left) and Professor Nick Wilson, of the Department of Public Health at the University of Otago, Wellington. Photo / Supplied

"They are in an improving condition in isolation, in a negative pressure room to prevent any spread of the disease," the spokesman said.

In a press conference last night, Health Minister David Clark said the person in their 60s had tested negative for coronavirus twice previously.

The first two tests were negative because they were from a throat sample. The symptoms of a lung infection were present though, so a third test performed.

Moving into the next phase

Baker told RNZ New Zealand was now moving into the containment or "stamp it out" phase.

Steps like contact tracing, and quarantining and observation of those people who contact with the person who tested positive were next - and underway, he said.

Director-General of Health Ashley Bloomfield said the risk of widespread infection was low at this point.

Three of the patient's family members were in isolation, and others on the flight would be contacted, he said.

"The people who the public health service will be contacting are the people who were in the same row as this individual or the two rows ahead or behind."

He said they would be required to self-isolate for 14 days and would be under regular communication with the public health units.

Baker said emerging research showed transmission in confined environments was limited.

"For example, we actually did research in 2009 with influenza, which was behaving very similarly ... and we found the only transmission on [a flight into New Zealand] was within two rows of the affected person. And other people found the same thing. So this is evidence-based public health."

The two negative tests for the coronavirus before the third positive test showed the importance of clinical judgment, he said.

"They're obviously very alert clinicians to this sort of possibility and they looked at the whole picture and they did more extensive testing.

"We hope that other clinicians - when they see cases [when a] result doesn't fit the clinical picture - will persist. And I think that's real credit to them".

Baker said a bigger problem than someone with the coronavirus returning a negative result was someone who had it but showed few symptoms.

"So they don't even see a doctor but they are infectious. And we know that the majority of people who are infected with this virus will have very mild symptoms. So that is a big problem in terms of containment."

For those concerned about the positive result, Baker said: "For the moment, it's really just business as usual across New Zealand. We're not looking at community transmission at all, as I think, has been pointed out.

WHO: No reason yet to call outbreak pandemic. Video / AP

"And that situation could well continue for weeks ahead. But at a certain point, it's going to become increasingly difficult to prevent widespread transmission in New Zealand as it is across the whole globe.

"Hopefully, we can delay that as long as possible. And we have to use this time for maximum preparation. And there are a whole lot of things that we can do and New Zealand is very fortunate to have the resources to have a very highly coordinated public health system and excellent health services."