Three high school students have tested positive for coronavirus across two Sydney schools as the number of infections throughout Australia's hardest-hit state continue to grow.

State health authorities confirmed that two Year 10 students from St Patrick's Marist College in Dundas, near Parramatta, and a Year 7 student from Willoughby Girls High School in Sydney's north shore had been diagnosed with COVID-19.

On Monday morning, parents were called to pick up their children from St Patrick's Marist College and a school spokesperson confirmed the campus would be closed on Tuesday.

NSW Health Minister Brad Hazzard said Willoughby Girls High School would also be forced to close for "at least one day".

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"Obviously when you have new cases at a school, it's cause for concern, because we want to make sure that we move as quickly as possible to require isolation of others who might have had contact with the confirmed cases," he said.

But parents picking up their children from Willoughby Girls High School on Monday morning said they weren’t too worried about the virus.

“The kids should be fine as long as they wash their hands," one mother told SBS News. “I’m not worried, her immune system is pretty strong, she takes nutritional supplements every day."

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Meanwhile, the Catholic Education Diocese of Parramatta, which manages St Patrick's Marist College, said they were working with the NSW Public Health team to identify staff and students who have had "close contact" with the infected teenagers.

Any students who will be required to self-isolate will be able to continue their studies from home, the spokesperson said.

The announcement follows the closure of Epping Boys' High School on Friday after a 16-year-old student was diagnosed with COVID-19. On Monday, the school reopened as almost 70 students and staff who had close contact with the infected student remained in self-isolation.

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NSW Education Minister Sarah Mitchell urged families from culturally and linguistically diverse communities not to panic.

“My advice to those communities is to take advice that comes from your school principal," she said.

"Our parents and families have been fantastic. The system is prepared. If your school does get in touch and suggest that children are kept home for a day or there's some isolation, just listen to the advice from [NSW] Health and the school.”

She added that the bulk of communications around coronavirus publicly are coming through NSW Health.

"I've certainly asked our department to make sure any specific advice that goes into school communities takes into account where those families are coming from and which languages are being used in the home, so there isn't any miscommunication," she said.

The number of coronavirus cases in New South Wales has jumped to 46, the highest of any Australian state.

Staff from St Vincent's Hospital in Sydney are also working to contact people who may have come into contact with a man confirmed to have COVID-19, after he visited the Darlinghurst emergency department on Friday night.

The man in his 70s had not recently travelled overseas before testing positive for the virus on Sunday, as Health Minister Greg Hunt told anyone who believed they had been exposed to someone with the virus to immediately self-isolate.

"Over the coming weeks and months, we will all be connected in some way, shape or form to people who contract the virus so we should be focusing on preparation," he said.

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"If you have flu symptoms or flu-like symptoms, then in the ordinary course of events then you wouldn't be presenting and if in doubt, get yourself tested."

Despite conceding that a rush of people would put "a little bit of stress" on the health system, he said the government would rather people "over-test than under-test" as the risk of locally transmitted cases grows.

The number of confirmed coronavirus cases in Australia is now 80, with at least 18 believed to have contracted the disease locally.

Victoria also reported three new cases of COVID-19 overnight, bringing the total number of confirmed cases in the state to 15.

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Two Australian Defence Force members were also confirmed to have contracted the virus and isolated on Sunday.

Across the globe, the number of confirmed COVID-19 cases has surpassed 109,000, with more than 3,800 deaths. The ASX also dropped by more than five per cent - or $110 billion - on Monday as panic over the outbreak continued.

Three Australians have so far died while confirmed to have the virus, including two residents of BaptistCare’s Dorothy Henderson Lodge aged-care home in northern Sydney.

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In a statement on Sunday, a BaptistCare spokesperson said they were "extremely saddened" by the death of an 82-year-old male resident, days after he tested positive for the coronavirus.

Last week, a 94-year-old female resident of the facility also died after contracting the virus.

“I have just recently spoken with the family and shared my condolences. As you can imagine, this is an incredibly difficult time for the family and for us all," BaptistCare CEO Ross Low said.

The first Australian fatality of the virus was Diamond Princess passenger James Kwan, 78, who died at Perth's Sir Charles Gairdner Hospital earlier this month.

Coronavirus symptoms can range from mild illness to pneumonia, according to the government's website, and can include a fever, coughing, sore throat, fatigue and shortness of breath.

People who are concerned they may have contracted the virus are advised to call their doctor before visiting or contact the national Coronavirus Health Information Hotline on 1800 020 080.