New Zealand reported its first local cases of the coronavirus in more than 100 days and put its largest city Auckland into lockdown to prevent another outbreak.

Authorities have detected four cases of COVID-19 in one household from an unknown source, and contact tracing is now underway to prevent further spread, Prime Minister Jacinda Ardern said late on Tuesday.

"Together we have beaten the virus before,” Ardern told a news conference. "We can do so again.”

From noon on Wednesday, Auckland will move to level 3 on New Zealand’s COVID alert system, signaling people should stay at home if possible and avoid contact with others. This will remain in place for three days, and the rest of the country will go to level 2 restrictions that include social distancing and limits on the size of gatherings.

The news comes after New Zealand recorded 102 days of no community transmission of COVID-19, managing to detect cases at the border with returned travelers going into mandatory quarantine. Health officials had warned it was only a matter of time before the virus returned.