NSW Premier Gladys Berejiklian said the decision was not taken lightly and is a precautionary response.
"Our first concern is for the health of the school's students, and it was decided that until we learned more about this specific case, the school should be closed as a precaution," Ms Berejiklian said.
"I'd encourage the community to remain calm at this time as the men and women in our health system continue their excellent work to minimise the impact of COVID-19."
Minister for Health Brad Hazzard said the NSW Government wants to ensure our citizens are kept as safe as possible from the challenges of the COVID-19 virus.
"We expect over the weekend there will be a detailed examination of where the student has been since he contracted the virus and with whom he has been in contact," Mr Hazzard said.
Minister for Education Sarah Mitchell said that the school community needs to remain calm and that more information will be available shortly.
"We have closed the school because it was the safest option, and have asked all students and staff to isolate themselves over the weekend. We will contact families and staff today and over the weekend to provide more information," Ms Mitchell said.
NSW Health will work with the Department of Education and the school to identify any close contacts of the Year 11 student. Close contacts need to stay at home and monitor themselves for symptoms for 14 days after their last exposure.
If you or your family become unwell, call HealthDirect on 1800 022 222, contact your GP or if significantly ill call ahead to an Emergency Department to be assessed.