St Pius X High School at Adamstown will be closed for the rest of the week after a student tested positive for coronavirus on Wednesday.
The school said its 1050 students and 140 staff had to self-isolate until they were informed by health officials they were not a close contact.
Hunter New England Health confirmed in a public health alert issed on Wednesday evening that the teenager was also a member of a Newcastle Jets Academy under-15 soccer team that played against the Stanmore Hawks at Arlington Oval in Dulwich Hill on Saturday.
The teenager's teammates and the members of the opposing team are considered close contacts and will be required to isolate for 14 days.
The health service urged anyone who attended the school on Monday to be on the lookout for COVID-19 symptoms and get tested if they developed.
The student caught the No.26 school bus from Hamilton to Adamstown at 8.20am on Monday morning.
HNEH said everyone on the bus would be required to isolate for 14 days and seek testing if symptoms developed.
The Newcastle Herald understands teachers were informed via email on Wednesday evening.
The Catholic School Office issued a statement on Wednesday night saying students had left the St Pius grounds before the CSO had been informed of the positive test.
"Parents and carers of all students at the school have been notified of the positive diagnosis today," the statement said.
"The school is working with NSW Health to identify 'close contacts' of the person with COVID-19.
"NSW Health will conduct contact tracing and will notify close contacts. Students and staff have been asked to self-isolate until receiving further advice from NSW Health or a communication from the school."
St Pius principal Robert Emery wrote to parents on Wednesday evening urging students to get tested if they developed COVID-19 symptoms.
He urged parents and students not to "speculate or speak to the media".
"We understand this incident will cause concern for students, families and staff alike.
"If you have any questions or concerns, I encourage you to contact either myself or our assistant principals.
"The safety, health and wellbeing of our school community remains paramount and we will do everything possible to limit the spread of COVID-19."
IN OTHER NEWS:
The Newcastle Herald understands the school has been proactive in implementing good hand hygiene during the pandemic and regularly wipes down desks.
Jets chief executive Lawrie McKinna said the club had shut down all teams' training late on Wednesday after being told by health officials of the positive test.
"That team will go into isolation, and coaches and team managers," he said. "None of the other teams have to go into isolation."
NSW reported 12 cases on Wednesday, a number Health Minister Brad Hazzard described as a "very good result", after testing 22,000 people in the 24 hours to 8pm on Tuesday.
Victoria recorded another grim record of 725 new cases and 15 deaths, one a man in his 30s.
NSW Premier Gladys Berejiklian announced on Wednesday that anyone travelling into NSW from Victoria would have to quarantine in a hotel for 14 days at their own expense from midnight tomorrow.
Labor Leader Jodi McKay backed the Premier's move but urged her to go further and introduce mandatory wearing of masks on public transport and in places of worship, supermarkets and shopping centres.
Queensland banned incoming travellers from all of NSW and the ACT as the east coast states moved to quarantine themselves from the Victorian domino effect.
Meanwhile, Wallsend Labor MP Sonia Hornery maintained her criticism of contact tracing in her electorate, writing on Facebook on Wednesday morning that more than 100 people had complained to her office that they should have heard from health authorities after a construction worker from Sydney visited three local watering holes last week.
"NSW Health advise they are only contacting people who actually signed into the Hotel Jesmond, Wallsend Diggers & Mezz Bar or the Lambton Park Hotel during the time the COVID positive man was present," she wrote.
"This means if you signed in to the venue 5 minutes before he did, you WONT be contacted, even if you sat directly beside him during dinner or at the bar.
"Not good enough I say. I will be following that up with the Minister."
Ms Hornery said on Tuesday that Newcastle needed "decisive action from the Premier on people travelling here from Sydney", one of whom turned out to be her Labor colleague, Upper House MP John Graham.
Mr Graham travelled to the city on Friday to talk to the media about grant allocations and to local stakeholders about the night-time economy, which is one of his shadow portfolios.
A spokesperson for Ms McKay would not comment about Mr Graham's visit but said state Labor had advised all staff to follow the NSW Health recommendation to avoid non-essential travel.
Flights stopped between Newcastle Airport and Melbourne several days after the Victorian bordered closed.
Virgin, Jetstar and Qantas are still flying to Queensland, but Qantas will stop on Tuesday. The other two carriers are monitoring demand.
An airport spokesperson said travellers could fly into Queensland until 1am Saturday without having to enter quarantine.