Sutherland Shire residents have been urged to come forward for testing even if they have only mild symptoms after a teacher at Laguna street Public School, Caringbah was diagnosed with coronavirus.
NSW Chief Medical Officer Dr Kerry Chant said the female teacher had "contacted a wide number of classes in the school, which necessitated the closure of the entire school" until June 25.
"Investigations are underway and ongoing into the source of infection for that teacher," Dr Chant said at a news conference.
"There is also uncertainty about the exact time of infectiousness, hence the precautionary approach."
Dr Chant said it was "critical" for people to come forward for testing as restrictions were eased.
"In particular, we are asking people in the Sutherland local government area to come forward for testing, irrespective of the severity of your symptoms," she said.
"If you have got mild symptoms, please come forward for testing as we are trying to unearth any undiagnosed transmission occurring in the community."
Dr Chant said it was also important that, even if someone has already been tested, they should present again if symptoms reoccurred.
There were nine new cases in NSW in the last 24-hour reporting period, but eight were overseas travellers, who are in hotel quarantine.
A staff member, who has had contact with most pupils at Laguna Street Public School, Caringbah, has tested positive for COVID-19.
The school will be closed for 10 days.
In a statement on Saturday night, Cronulla MP and Attorney-General Mark Speakman said school principal Rosie Di Mattia emailed parents and carers with the news this evening.
"The staff member has had contact with most students at the school," he said. "As a result, the school will be closed until Thursday 25 June.
"From Monday, the school will provide learning from home materials for their students.
"NSW Health and the Department of Education have a refined and rigorous process when a member of a school community tests positive for the virus.
"I urge all parents, students and staff to listen to the directions of the Department of Education and NSW Health so that everyone can return to school by Thursday 25 June.
"On any given weekday, one in five people across NSW will attend a school site.
"Unfortunately this means that occasionally schools will be impacted by COVID-19 while it still exists in the community."
The Education Department said the school had commenced contact tracing.
"Upon advice from NSW Health, all students at the school have been deemed as a close contact and should commence self-isolating," the department said.
"The staff member has had contact with most students at the school during the period they may have been infectious and the decision was made in consultation with NSW Health to cease onsite learning at the school until 24 June 2020.
"The school will resume onsite learning on Thursday the 25th of June 2020.
"NSW Health will contact all families of the children enrolled at the school over the next 1-3 days to confirm this information, provide them with details about their period of isolation, and answer any questions.
"While we recognise this will be disruptive and inconvenient for many families, it is important that we follow NSW Health advice and take all necessary precautions to minimize the risk of further transmission to support the vulnerable members of our community.
"We take great pride in the way that as a school community we have worked together during these challenging times and seek your support again in working with us as students and staff resume learning from home.
"NSW Health has requested anyone who has been unwell or has flu-like symptoms to be tested at one of the COVID-19 clinics that can conduct testing for school-aged children.
"The Sutherland COVID 19 Drive-Through Testing Centre is located at Sutherland Multi-Purpose Community Centre 123 Flora St Street Sutherland. Sutherland Hospital has a COVID clinic.
"Further information on COVID-19 is available on the NSW Health website.
"Laguna Street Public School will be non-operational for on-site learning from Monday 15 June 2020 to Wednesday 24 June 2020.
"Students and staff will return for on-site learning from Thursday 25 June 2020.
"In line with departmental guidelines the school will be cleaned thoroughly. Primary OSHCare will not be operational during this learning from home period.
"From Tuesday 16 June 2020 teachers and staff will support students with their educational continuity through our learning from home arrangements.
"Information about how our learning from home program will be managed will be sent to you on Monday 15 June 2020. Online learning materials are still available through the department's Learning from home site.
"The safety and wellbeing of our staff and students is of paramount importance to us at all times. As such we will continue to work closely with NSW Health to ensure that all necessary health advice is adhered to and to protect the vulnerable members of our community.
"Thank you for your ongoing support."