New Zealand was hit with its first untraceable case of COVID-19 since August on Thursday.
An Auckland woman in her 20s tested positive and authorities could find no link to other cases, director of public health Caroline McElnay told a press conference.
Workers in the central business district of Auckland have been asked to work from home as authorities investigate the source of the mystery infection.
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What are the details of the case?
The woman lives next to a managed isolation hotel, which was evacuated due to a fire alarm earlier in the week. However, despite concerns that those quarantined may have mingled with the public, the woman developed symptoms before the evacuation.
McElnay said the shop assistant and student had received advice to isolate. However, after speaking with her manager, she went in to work in a customer-facing role with a mask.
Local media reported that she also took trips in Ubers, and those drivers had been contacted. A colleague and two friends were also reportedly asked to isolate and were tested.
Residents of the woman's apartment building were also tested and asked to stay home, and the building was being deep cleaned, Radio NZ reported. Authorities were reportedly genome-testing her infection to try and establish a link to other cases.
What's the coronavirus situation in New Zealand?
COVID-19 Response Minister Chris Hipkins said New Zealand was still in a "very strong" position to contain the virus. Authorities did not raise the alert level for the nation or impose new mandatory restrictions.
Hipkins said the situation was disappointing and asked employers to be "good" and allow workers to stay home if they were sick, public broadcaster Radio NZ reported.
Two other cases were reported on Thursday, both linked to the border. They brought the country's total to 1,635 cases, with 53 active cases.
New Zealand has thus far enjoyed tremendous success in controlling the pandemic, with virtually no community spread.
aw/rt (dpa, AP)