The coronavirus cluster in Sydney's Northern Beaches has jumped to 17 new infections, prompting health authorities to ask residents in the area to temporarily stay home.
NSW Health on Thursday evening confirmed 17 COVID-19 cases have now been identified in the area, including those diagnosed on Wednesday and Thursday.
Earlier in the day, authorities put the number of virus cases linked to the cluster at five.
"As a number of new cases are currently being interviewed, it is likely that a number of new venues will be identified and that people in the Northern Beaches may have attended these venues," it said.
For the next three days, people in the Northern Beaches Local Government Area are being advised to stay at home as much as possible and to avoid unnecessary travel outside the area.
Residents are asked not to visit friends or family in aged care facilities or hospitals unless essential, and to avoid high-risk venues including clubs, restaurants, churches and gyms.
People should also avoid unnecessary travel to the Northern Beaches.
Health authorities detailed three new COVID-19 cases in the Northern Beaches on Thursday morning - a woman in her 50s who works at Pittwater Palms aged care facility at Avalon Beach, her partner and a Frenchs Forest man in his 60s who plays the drums for band Nothing-Too Serious.
Chief Health Officer Kerry Chant said her department's hypothesis was that an unknown person infected the drummer, a woman in her 60s and man in his 70s at Avalon RSL last Friday where Nothing-Too Serious was performing.
The woman in her 60s then attended Avalon Bowlo on Sunday, where she infected the woman in her 50s, who in turn infected her partner.
Genomic testing would be completed by Thursday night, Dr Chant said.
Sewage testing last Thursday uncovered no virus fragments in the area, indicating the virus was newly introduced.
"The working hypothesis is that there was an unknown person present at Avalon RSL that was the source of infection, given we've got three people at least ... that's potentially the exposure source," Dr Chant told reporters.
The drummer also played at Penrith RSL on Sunday and at the Kirribilli Club on Monday.
Health alerts have been issued for those two venues, Avalon RSL and numerous others across Sydney's Northern Beaches.
The cluster has led WA Premier Mark McGowan to order any arrivals in his state who were in NSW from 11 December to self-isolate until they test negative.
"Anyone arriving directly from Sydney Airport or from another Australian airport having been in NSW on or after 11 December, from this point forward must take a COVID-19 test, either at Perth Airport on arrival, or at another COVID clinic within 24 hours, and follow the same self-quarantine requirement until a negative test result is confirmed," Mr McGowan said.
Hundreds of people started queuing up at Mona Vale hospital early on Thursday to get tested for the virus, with multiple pop-up testing centres now in place.
Premier Gladys Berejiklian also flagged on Thursday some Northern Beaches nursing homes may be locked down until the outbreak is contained.
"We want to get on top of this and don't want this concering us in the last few days before Christmas," she told reporters.
"There are a number of aged care facilities which are very vulnerable in the northern beaches, so (NSW Health) will also be issuing a directive to say (to) certain aged care facilities on the Northern Beaches, we're recommending no visitors until we identify the source of the infection and feel more confident that we have it under control."
The latest outbreak has also prompted concerns about whether the recently-opened Queensland and WA borders will again be shut to people from NSW over Christmas.
NSW Premier Gladys Berejiklian addresses media during a COVID-19 update in Sydney. Source: AAP
Mr Hazzard implored the two states to avoid "pre-emptive" action.
"My blood pressure hasn't gone up, my pulse hasn't gone up, we're just doing what we do in NSW - handling the cases," he told reporters.
It comes a day after authorities announced that after working to transfer international aircrew to their accommodation.
With additional reporting by AAP.
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If you are experiencing cold or flu symptoms, stay home and arrange a test by calling your doctor or contact the Coronavirus Health Information Hotline on 1800 020 080.
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