Health Minister Brad Hazzard on Monday said two year 10 students from St Patrick's Marist College in Dundas were confirmed to have COVID-19 as well as a year 7 pupil from Willoughby Girls High School.

The year 7 student's mother has also been diagnosed with the virus.

They are among six new cases of the virus in NSW with two men in their 50s also diagnosed. There are 46 confirmed cases in the state.

"When you have cases at a school, it is cause for concern because we want to make sure that we move as quickly as possible to require the isolation of others who might have had contact with the confirmed case," Mr Hazzard told reporters on Monday.

The co-ed St Patrick's Marist College will be closed on Tuesday, the school said in a statement.

Willoughby Girls High School is "temporarily" closed from Monday due to a confirmed case of COVID-19, it said in a statement.

NSW Health is working with staff and students at both schools to determine who the confirmed cases have been in close contact with.

Mr Hazzard says there is no concern "at this point" for Premier Gladys Berejiklian who visited Willoughby Girls on February 24.

"She has been taking some of the precautions in terms of stopping the handshakes and perhaps not doing those hugs that she normally does, because she's a very warm person," he said.

"I think she would not be the slightest fussed."

The health minister urged people to remain calm after two women were charged over a fight which broke out in a Sydney supermarket over toilet paper at the weekend.

"This is not a situation for overreaction, it's not a situation for being rude or offensive," Mr Hazzard said.

"We're all in this together. We're doing pretty well. But just be polite and be courteous and careful."

The minister said the majority of cases in NSW are people who have recently travelled overseas, but he anticipates an increase in community transmission as the virus progresses.

"It is a challenging time for all of us," he said.

"We can anticipate it will be quite active here, although thus far, NSW and Australia are doing extraordinarily well compared to the rest of the world."

Meanwhile, Epping Boys High School in Sydney re-opened on Monday after a one-day closure on Friday because a 16-year-old student was diagnosed with the virus.

The school said on Facebook that the education department and NSW Health have been working to identify all people who had close contact with the year 11 student.

They're being asked to self-isolate for 14 days.

NSW Health said St Vincent's Hospital in Sydney is also contacting patients after a man in his 70s visited the emergency department on Friday and was diagnosed with COVID-19.

Authorities on Sunday confirmed the death of an 82-year-old man who contracted the coronavirus from an infected aged care worker at BaptistCare's Dorothy Henderson Lodge in Sydney.

His death follows that of a 95-year-old woman - a fellow Dorothy Henderson Lodge resident - and a 78-year-old man in Perth who'd been on the Diamond Princess cruise ship.

Australian Associated Press