NSW health authorities are still working to trace the source of a 17-strong coronavirus cluster developing at an independent Catholic school in northwest Sydney.
At least six new COVID-19 cases were linked on Tuesday to Tangara School for Girls in Cherrybrook, following the previous identification of 11 cases.
NSW recorded 22 new coronavirus cases in the 24 hours to 8pm on Monday - four of which are in hotel quarantine, another two are linked to Victoria and eight from the Tangara cluster. Two of those eight Tangara cases had been identified on Monday.
It's the highest daily increase of COVID-19 cases in NSW for almost four months, with 17 locally acquired cases being the highest number in that category since late July.
The Opus Dei-associated Tangara has closed its secondary campus until August 24 and its junior campus until at least Wednesday after its first COVID-19 case last week.
NSW Health on Tuesday said the source of the Tangara outbreak remained unclear and all secondary students and staff were in self-isolation and being tested.
Another primary school, Parramatta Public School, will close on Wednesday for deep cleaning after a student tested positive to COVID-19.
The Independent Education Union of Australia is urging the NSW government to mandate mask use in schools for staff and senior students.
"The IEU is concerned that our members and the young people in their charge are being told there is something exceptional about passing through the school gates that means the COVID-safe precautions we are all undertaking out in the wider community need no longer apply," IEUA NSW secretary Mark Northam said in a statement on Tuesday.
In western Sydney, Bonnyrigg Heights Public School reopened on Tuesday after being closed for cleaning on Monday after a primary school student tested positive, but Kids' Early Learning Quakers Hill remains closed after children were exposed to the virus.
A second student at Our Lady of Mercy College in Parramatta has also caught COVID-19.
After three weeks with no new COVID-19 cases linked to the Batemans Bay Soldiers Club cluster in NSW's south, the local high school and public school were both closed on Tuesday after one student at each school tested positive for the virus.
NSW Chief Health Officer Kerry Chant has urged people to avoid large gatherings and this week admitted older school students are more likely to transmit the virus.
Premier Gladys Berejiklian said the state remained on high alert.
"We are in a pandemic - every organisation, every entity needs to abide by the COVID-safe plans," Ms Berejiklian told reporters on Tuesday.
"My anxiety has not subsided in relation to what a knife edge NSW is on, but we need to keep pulling together and keep doing the right thing.
"I don't want people living with the guilt of passing on the disease or causing the spread because they could've prevented something from happening."
Wildginger restaurant in Huskisson near Jervis Bay also confirmed on Tuesday that two patrons on August 8 have since come down with COVID-19. The restaurant said it would close for two weeks while staff are in self-isolation.
Eight COVID-19 patients in NSW are currently in intensive care, with six ventilated.