NSW has recorded its highest daily number of coronavirus infections in almost four months, as the cluster linked to a school in Sydney's north-west continues to rise.
There have been 22 new infections in the state, including eight linked to Tangara School for Girls in Cherrybrook.
The last figure this high was on April 16, with 29 cases.
Tangara School has now recorded 17 confirmed cases since the first infection was discovered in a student on Thursday.
NSW Premier Gladys Berejiklian said "at least a third" of Tuesday's cases are from the Tangara School cluster.
Yesterday, NSW Health said there were nine cases linked to the school.
Of the total cases, 11 students, four teachers and two social contacts of school community members have been linked to the outbreak.
The ABC understands some students attended a camp, which has become a focus for contact tracers.
The original source of the cluster remains unknown, but Ms Berejiklian reiterated a warning to non-government schools that they must stick to coronavirus restrictions.
"Schools, in particular non-government schools, cannot undertake those extra-curricular activities that you do outside of a pandemic — and I can't make that message stronger."
She said institutions needed to make sure there were no off-site gatherings where mingling could occur.
"Every organisation, every entity needs to abide by the COVID-Safe plans, because otherwise we risk having a surge in numbers [and] new clusters, and no one wants to see that."
The school's senior campus will be closed until August 22, but the junior campus will reopen tomorrow.
"All students, staff and support staff at the secondary school must self-isolate for 14 days and get tested, regardless of symptoms," NSW Health's Dr Jeremy McAnulty said.
"Students at the primary school must monitor for symptoms and get tested if symptoms develop."
NSW Health Minister Brad Hazzard said the source was a concern.
"At this stage further investigation will, perhaps, give us further clarity at how that's all occurred," Mr Hazzard said.
"It's not always possible to determine the source and that's what worries us most."
The Premier said four of the 22 new cases were returned international travellers in hotel quarantine, while another two acquired their infections in Victoria.
"It is a daily battle in NSW, we have to be on our toes, we are in a state of high alert," Ms Berejiklian said.
"My anxiety has not subsided in relation to what a knife edge NSW is on."
The Premier also defended the health department's response to the coronavirus outbreak at Newmarch House aged care home in Western Sydney.
Yesterday, it was revealed through email correspondence sent between NSW Health and the Federal Government that the former resisted moves to transfer infected patients to hospital.
The Premier said there wasn't a "one size fits all policy" to managing elderly patients.
"Health experts always need to provide advice based on the individual's needs," Ms Berejiklian said.
"Some residents, it's traumatic taking them out of what is their home."
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