Northern Sydney virus cluster jumps to 17

Fifteen new cases were identified on Thursday, with health authorities urging locals to stay at home as much as possible over the next three days.

NSW Health says residents should not visit hospitals and aged care facilities unless essential, avoid unnecessary gatherings, keep to their household groups, and avoid high-risk venues like gyms.

People should avoid unnecessary travel to the Northern Beaches and people living there should avoid leaving.

The new cases are still being interviewed and more cases will probably be identified, NSW Health warns.

Authorities are investigating a potential super-spreader event at a local RSL, Chief Health Officer Kerry Chant says.

Health authorities detailed three new cases 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.

Dr 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.

NSW Health revealed an additional nine cases had been identified on Thursday afternoon.

The cluster has led WA Premier Mark McGowan to order any arrivals in his state who were in NSW from December 11 to self-isolate until they test negative.

Hundreds of people started queuing at Mona Vale Hospital early on Thursday to get tested for the virus and multiple pop-up testing centres are now in place, including at Avalon, Newport and Frenchs Forest.

Premier Gladys Berejiklian flagged Northern Beaches nursing homes will be locked down until the outbreak is contained, just a week after restrictions eased allowing unlimited visitors.

"We want to get on top of this and don't want this concerning us in the last few days before Christmas," Ms Berejiklian told reporters.

"There are a number of aged care facilities which are very vulnerable in the northern beaches ... we're recommending no visitors until we identify the source of the infection and feel more confident we have it under control."

The Pittwater Palms aged care facility is closed to visitors while residents and staff who had been in contact with the infected worker were being tested and were self-isolating.

The latest outbreak has prompted concerns the recently-opened Queensland and WA borders will again shut to people from NSW.

Health Minister Brad Hazzard has implored the two states to avoid "pre-emptive" action, saying NSW would quickly squash the cluster.

Tasmania nevertheless elected on Thursday to ban anyone who had visited the venues on NSW's health alert list from entering the island state. Those in NSW who are set to travel to Tasmania must also reapply for their e-Travel pass.

The Northern Beaches cases were uncovered after a 45-year-old van driver transporting international air crew members to and from Sydney Airport was on Wednesday confirmed to be COVID-positive.

The southwest Sydney man wore a mask, worked only with air crew members and was not involved in regular taxi services for the public.

Australian Associated Press