The outbreak has grown to 30 people and extended beyond Auckland for the first time.
Until the cluster was discovered on Tuesday, New Zealand had gone 102 days without infections spreading in the community. The only known cases were travellers quarantined after arriving from abroad.
Together, we have got rid of Covid before. We have kept it out for 102 days, longer than any other country. We have been world-leading in our Covid response, with the result that many lives were saved and our economy was getting going faster than almost anywhere else. We can do all of that again
Health authorities believe the virus must have been reintroduced from overseas, but genome testing has not found a link with any of the quarantined travellers.
That has prompted authorities to investigate whether shipping workers were a source, after several employees at a food storage facility were infected.
Prime Minister Jacinda Ardern said extending the Auckland lockdown, which began on Wednesday, would give authorities time to get a handle on the virus cluster and isolate those infected.
“Together, we have got rid of Covid before,” she said in a highly anticipated address. “We have kept it out for 102 days, longer than any other country. We have been world-leading in our Covid response, with the result that many lives were saved and our economy was getting going faster than almost anywhere else. We can do all of that again.”
All of the new cases in the outbreak appear to be linked through family or work connections.
The only known infections outside Auckland are two people in the central North Island town of Tokoroa who were visited by infected family members from Auckland.
Officials said they thought the chances were low that the virus would spread further there.
Several of those infected work at an Americold food storage facility in the Auckland suburb of Mount Wellington.
Officials are looking at the possibility that workers on a freight ship or at the port may have spread the infections, despite physical distancing requirements at those sites and orders preventing ship workers coming ashore.
Director-general of health Ashley Bloomfield said rigorous testing is being carried out “as part of our investigation just to follow that chain of the Americold goods that might have come in through the port and been transported to that Mount Wellington depot”.
Officials are also investigating the possibility that the virus could have survived from abroad on chilled or frozen food boxes and then infected workers in New Zealand, a scenario they consider unlikely.
Mr Bloomfield said they completed a record of more than 15,000 tests on Thursday and they were getting a clearer picture of the outbreak’s contours.
Health Minister Chris Hipkins said: “All of the cases so far, at this point, are connected. They are all part of one Auckland-based cluster. And that is good news.”
The outbreak has cast doubt on whether New Zealand’s general election will go ahead as planned next month and has halted political campaigning.
Ms Ardern said she would decide by Sunday on whether to delay the poll, which she can defer by up to about two months under New Zealand law.
Opinion polls indicate that her Labour Party is likely to win a second term.
