Earlier this week, the government placed Auckland under its second-highest Alert Level 3 lockdown through Friday. Ardern extended the measures for another 12 days.
"Together, we have got rid of COVID before," she said during an evening news conference.
"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."
The New Zealand Ministry of Health reported 12 new cases of the novel coronavirus and one probable case Friday. All except one were linked to existing cases.
The new cases increase New Zealand's latest outbreak of the virus to 29. Since the start of the pandemic, the country has had 1,251 cases and 22 deaths.
Public health officials are encouraging those who test positive and their families to move to a local quarantine facility to limit the spread.
Auckland Mayor Phil Goff called the re-emergence of the virus in his city "devastating."
"However, we know from experience that going hard and going early is the best way to stop COVID-19's spread," he said. "I welcome the fact that we are not going back to a Level 4 lockdown. But even at Level 3 I know this means personal sacrifices for people and for businesses and I thank Aucklanders for that."
Under the Level 3 lockdown, all public venues must close, employees must work from home, elective services at hospitals are deferred, domestic travel is limited and people may only leave their homes for essential reasons, such as groceries.