Microbiologist Siouxsie Wiles has assured New Zealanders they shouldn't be worried about the six historical cases of COVID-19.
The Ministry of Health announced the cases on Wednesday at 1pm along with three in the community.
The historical cases include one confirmed case dating back to February and five probable cases connected to the confirmed case.
"At the time, they did not meet the case definition for testing," the ministry said.
On Wednesday afternoon Dr Wiles confirmed the historical cases are "nothing for New Zealanders to be worried about".
"Such cases have been found in many other countries and are because we now know that the COVID-19 virus was already beginning to infect people in parts of Europe while the world was focused on the growing outbreak in China," she said.
"We may yet see more of these cases though it will still only amount to a small fraction of New Zealanders. The rest of us remain very much susceptible to this virus."
Dr Wiles emphasised testing is a crucial part of New Zealand's "test-trace-isolate strategy" and Kiwis experiencing symptoms should get tested for COVID-19.
"I urge everyone who experiences symptoms that could be COVID-19, from a loss of smell to a runny nose, fever, dry cough, or shortness of breath, to get tested as soon as those symptoms start. If it is COVID-19, any delays mean more contacts and potentially more spread of the virus."
New Zealand currently has 1468 confirmed cases of COVID-19 and has recorded 25 deaths.
The country's first case was reported on February 28, but the confirmed historical case first reported symptoms on February 21.
"This would mean that the infected family member from Italy is effectively now the first case we are aware of in New Zealand," the ministry said.
"Consequently, the other household cases would represent the first locally acquired cases of COVID-19 in New Zealand, given the onset of symptoms from February 29 for the confirmed case. Further investigation will continue."