SYDNEY, Dec. 17 (Xinhua) -- A cluster of five new COVID-19 cases in Sydney's north threatened to unravel the city's success in containing the virus, with authorities warning anyone in the area with even the mildest of symptoms to get tested.

Two cases with no known source were identified on Sydney's Northern Beaches on Wednesday, with a further three infections confirmed by health officials on Thursday.

Another man who worked at Sydney Airport driving international air crews tested positive on Tuesday, although he is not believed to be linked to the other cases.

"At the moment we are still unclear about the exact source of the (outbreak) and are awaiting genome sequencing," New South Wales (NSW) Chief Health Officer Dr Kerry Chant said.

One of the new cases is a woman in her 50s who works at an aged care facility and is believed to have had close contact with a number of residents, while another is a man who played in a band at several venues across the city.

"Interestingly the band is called Nothing Too Serious... certainly from our point of view I wouldn't say it's exactly how we feel because it obviously is serious," NSW Health Minister Brad Hazzard said.

Previously Sydney had gone without a case of local infection for nearly two weeks, although the virus was regularly detected in travellers returning from overseas who were already in hotel quarantine.

COVID-19 restrictions were recently eased across much of Australia including the reopening of domestic borders and a significant relaxing of rules for bars and restaurants across major cities.

Large volumes of people turned out to be tested in Sydney's north on Thursday morning with an additional pop up clinic being rapidly established to cope with demand.