Residents from Queensland, Victoria and New South Wales are being urged to get tested for COVID-19 after traces of the virus were found at sewage plants.
Viral fragments in wastewater can be due to people who have recovered from COVID-19 continuing to 'shed' the virus, the Victoria Health Department said.
While they may not be considered infectious, it can take several weeks for someone to stop 'shedding' the virus.
The Victoria Health Department is urging anyone with any symptoms of COVID-19 to get tested as the city remains on high alert after a five-day lockdown.
The recent community cases in south Auckland have prompted New Zealand's Institute of Environmental Science and Research (ESR) to carry out wastewater tests.
Samples taken at four Auckland sites on February 18 have all returned negative results, the Ministry of Health (MoH) confirmed on Saturday.
The MoH says sampling is a complement to community testing.
"Any positive results would be carefully checked to determine what action would be required," a MoH spokesperson told Newshub.
"In most instances, it would likely prompt additional community testing if it was thought the wastewater sampling had detected COVID-19 where the source could not be easily determined."