New Zealand declared on Aug. 11 that it was shutting down its largest city after four new cases of Covid-19 were discovered in Auckland.

Four community cases in Auckland, cases travelled out of city and went to work

It is the first evidence of domestic transmission in the country after New Zealand was free of Covid-19 for 102 days.

The four cases discovered all belong to one household, but authorities were unable to pinpoint the origin of the outbreak.

In addition, it was reported that two of the cases travelled to Rotorua and visited a number of tourist spots.

They also went to work while they were symptomatic, reported NZ Herald.

If there is another case in Rotorua, a nationwide response will be necessary, said New Zealand's director general of health Ashley Bloomfield, urging people in Rotorua to stay vigilant.

NZ's largest city in soft lockdown

Auckland residents will be undergoing mass testing for the next three days, with the city in a soft lockdown mode as of 12pm, Aug. 12 (8am Singapore time).

Aucklanders are instructed to stay home other than for essential personal movement.

The rest of New Zealand will be placed under level two restrictions, where people are not allowed to gather in groups of more than 100.

"These are very significant decisions, New Zealand prime minister Jacinda Ardern said. "Moving an entire city, and New Zealand's largest city, into level three restrictions is not a decision we take lightly."

"We need to make sure we have as much information as possible."

"This move means we can be cautious but also make sure we have more information before we make any decisions that have a longer-term impact," Ardern explained.

Auckland may remain in lockdown for 7 weeks in worst-case scenario

Epidemiologist Michael Baker told NZ Herald that the city of Auckland may remain in lockdown for seven weeks in a worst-case scenario.

"You would expect a longer lockdown would be more likely. The most positive outcome is if contact tracing identifies a clear line of transmission from an imported case or someone working at managed quarantine," Baker said.

Shaun Hendy, a physicist from Auckland University, highlighted that the duration of the outbreak would depend on whether the links of transmission can be identified.

"If we can identify that, then that possibly gives us the chance of a more localised and shorter lockdown," Hendy said.

"If we're unable to do that people should be preparing themselves for a longer lockdown period."

He added that it was likely for the virus to be outside of Auckland as well, and cautioned New Zealanders across the country to act as if the disease is present in the community.

Top image via Hagen Hopkins/Getty Images