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The detection of four new infected family members earlier this week shocked a country that had recorded no locally transmitted cases for more than three months, reports BBC.
Of the new cases, 13 have been linked back to this family, while one is an overseas arrival who was in quarantine.
A three-day lockdown was imposed in Auckland on Wednesday.
"We can see the seriousness of the situation we are in," Prime Minister Jacinda Ardern said in a news conference.
"It’s being dealt with in an urgent but calm and methodical way."
New Zealand has been internationally praised for its early response to the pandemic.
It has again moved swiftly to reimpose strict movement restrictions in Auckland and social distancing measures across the country.
Before Tuesday, New Zealand went 102 days without recording a locally transmitted case of Covid-19, one of the few countries to reach such a milestone.
Ms Ardern has also said she expected the outbreak to grow further before it slows down.