Seven new COVID-19 cases in NSW have had their link to a southwest Sydney pub cluster confirmed, bringing the total of associated cases to at least 40.
NSW Health reported 10 new COVID-19 cases in the 24 hours to 8pm on Wednesday from almost 23,000 tests, with six cases locally acquired.
Three of the six cases are connected to the Crossroads Hotel in Casula, which an infected Melbourne man attended on July 3, and the other three are of unknown origin.
An additional four cases after the 8pm deadline have been connected to the hotel including a child of a known case, a man in his 30s who was a contact of a known case, a male patron in his 80s and a teen who attended Hurricane Grill in Brighton-Le-Sands with a known case.
At least 21 of the 40-plus cases in the cluster were hotel patrons.
NSW Chief Health Officer Kerry Chant said another case confirmed after 8pm on Wednesday involved a NSW man who on July 12 returned to Ballina from Melbourne on Jetstar flight JQ466, with passengers on that flight being contact traced.
The passenger was wearing a mask on the flight and has since been self-isolating.
"People are infectious prior to symptom onset and in some cases the symptoms are incredibly mild, people might not even recognise (them) unless you're thoroughly interviewed and really teasing out your health status," Dr Chant told reporters.
"None of this is around the actions of individuals but collectively we need to be vigilant."
Dr Chant earlier this week warned COVID-19 clusters would pop up because of the "stealthy" nature of the virus and the rapidity with which the virus could spread.
NSW Health on Wednesday confirmed the "patient zero" of the outbreak was most likely a Melbourne freight company employee who attended the Crossroads Hotel on July 3 for a work party. At least six of his colleagues have since caught COVID-19.
The man entered NSW on June 30, before the state's border with Victoria closed.
NSW Health Minister Brad Hazzard told 2GB radio on Thursday that young Australians needed to keep in mind the consequences of their actions amid the pandemic.
"They can be super-spreaders with great skill and acumen," he said.
"We've got a young bloke from that latest (Crossroads Hotel) cluster ... he had one of the highest infection levels that we've ever seen."
NSW Health on Wednesday also named several venues where confirmed COVID-19 cases spent time, including the YMCA at Revesby, Wests Leagues Club at Leumeah, Macarthur Tavern in Campbelltown, the Picton Hotel and Casula Kmart.
The Milky Lane burger joint in Parramatta and the Bavarian Macarthur restaurant in Campbelltown were later added to the list, as well as Woolworths in Bowral.
At least four gym-goers at Planet Fitness in Casula have also come down with COVID-19 and the company said in a statement on Thursday it was working with NSW Health.
"Since first hearing a patron with COVID-19 attended the facility, Planet Fitness has been extremely proactive with closing the facility, undertaking a deep clean and advising gym users who were present at the time to immediately get tested," chief executive Barrie Elvish said.