Covid-19 has been detected in a wastewater sample taken in Tairāwhiti/Gisborne on December 6, the Ministry of Health said in Wednesday's 1pm update.
This follows positive detections on December 1 and 2.
In a statement, the ministry said public health officials are not aware of any recovered cases in the region who may be shedding the virus.
"A third positive detection strongly indicates that there is at least one undetected case in the community."
The ministry says two further samples will be collected this week.
Tairāwhiti DHB has the second lowest number of fully vaccinated people in New Zealand, with an 80 per cent uptake of two doses of the Covid-19 vaccine.
The number of people in the region who are partially vaccinated currently sits at 89 per cent.
Anyone living in the Gisborne area with any symptoms that could be Covid-19 is encouraged to get a test.
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