St Christopher's Catholic Primary School in Panania in Sydney's south-west is closed on Monday after a person who attended an event hosted by the school tested positive for COVID-19.
Sydney Catholic Schools executive director Tony Farley said the professional development event was held on 12 March and the infected person was not a teacher at the Panania primary school or any other Sydney Catholic school.
"Closing a school, even for just one day, may seem to be an extraordinary measure but we are living in extraordinary times," Mr Farley said.
The school will undergo a thorough "hygiene sweep" on Monday and teachers who attended the professional development event have been asked to get tested and self-isolate as a precaution.
The school will reopen on Tuesday.
NSW schools from Monday are adopting social distancing measures, including cancelling assemblies, excursions, and travel, as well as some events and conferences in a bid to slow the spread of COVID-19.
The vast majority of schools around Australia are remaining open during the outbreak.
On Sunday, Prime Minister Scott Morrison said the broad closure of schools "could make the situation worse, not better".
"When you take children out of schools and put them in the broader community, the ability for them to potentially engage with others increases that risk," he told reporters.
Prime Minister Scott Morrison discuss possible outbreak scenarios on Sunday. Source: AAP
He also said nurses and doctors could be impacted as "they would have to remain home and look after their children".
Australia's COVID-19 death toll rose to five on Sunday after a 90-year-old woman who was a resident of Sydney's Dorothy Henderson Lodge nursing home died.
She is the third resident of the nursing home who has died after becoming infected with COVID-19.
