NSW Health authorities are still trying to track the source of the Batemans Bay Soldiers Club coronavirus cluster.
NSW chief health officer Kerry Chant said authorities would do genomic sequencing in an attempt to track it down.
But she said the "jigsaw puzzle sometimes has empty black spaces" despite the best detective work.
The cluster stands at eight people, only one of whom is a local resident.
Four cases from one family were diagnosed earlier and another four in the 24 hours to Sunday night.
One is a staff member, two had a meal there and one was a contact, NSW health authorities said on Monday.
Anyone who was at the club on Monday July 13, or on Wednesday, Thursday and Friday, July 15 to 17, has been ordered to immediately self-isolate for 14 days, get tested even without symptoms, and stay isolated even with a negative test.
NSW Health said, "Everyone must stay in isolation for a full 14 days even if their test is negative. Anyone who develops COVID-19 symptoms should also be retested, even if they have had a negative result previously."
For Tuesday July 14, people are not ordered to self-isolate, but are asked to monitor for symptoms.
NSW reported 20 new cases in the 24 hours to 8pm on Sunday, all linked to known clusters - the Crossroads Hotel (now 48 cases), the Thai Rock restaurant and the Batemans Bay Soldiers Club.
NSW Premier Gladys Berejiklian said the next few weeks were critical. She urged people to avoid large crowds and think twice about going into any crowded place even with social distancing.
"I cant say enough how stressed and worried I am about the next few weeks," she said.
"We are at a critical point in our state's ability to deal with the pandemic ...
"All of us have to really think about what we're doing in the next few weeks. The next few weeks are absolutely critical."
If NSW got through the next three for four weeks and stayed on top of the seeding from Victoria and current outbreaks, the state could have "medium to long term surety" that it could keep moving forward, she said.
NSW has two people intensive care, one aged in their 30s.
NSW Police Minister David Elliott said there were particular concerns for the south coast community.
"The concern in Batemans Bay is the ageing population down there and the transient nature over the school holidays of the population," he told the Seven Network on Monday.
"Make sure you don't put yourself in a position or situation where you can pass [the virus] on."
NSW Health outlined where people could get tested.
"To ensure people can get tested quickly, Southern NSW Local Health District (LHD) will continue testing in Batemans Bay through a COVID-19 pop-up clinic at the Hanging Rock Oval Car Park (near the function centre) on Beach Road, Batemans Bay. An additional pop-up clinic will be operational in Batemans Bay from the morning of Monday 20 July to further boost testing capacity.
"Anyone feeling unwell - even with the mildest of symptoms such as a runny nose or scratchy throat - is urged to seek testing and self-isolate. Do not go to work or catch public transport until you are cleared of COVID-19.
"Additional clinics in the LHD include Goulburn Base Hospital, Queanbeyan District Hospital, Eurobodalla Health Service (Moruya), South East Regional Hospital, Cooma District Hospital, Jindabyne Clinic and Yass District Hospital, with pop-up clinics at Malua Bay, Merimbula and Crookwell."
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