NSW Health and Education says the one day closure at Epping Boys High School on Friday will enable the school community and health officials to work through a contact and containment strategy.

The case brings the number of confirmed cases in NSW to 25.

"We are immediately establishing contact with all new cases and their families, as well as their close contacts and advising them to self-isolate for 14 days, monitor their health and be tested for COVID-19 should they become unwell," NSW Chief Health Officer Dr Kerry Chant said.

The secretary of education, Mark Scott, the department had prepared continuity plans and was contacting students, parents and the broader school community to provide advice and support.

Meanwhile, group visits by children to nursing homes have been barred after more than a dozen youngsters attended a Sydney aged care facility where an elderly coronavirus-infected woman died.

About 17 children from Banksia Cottage childcare centre will be assessed for COVID-19 after visiting residents at the nearby Dorothy Henderson Lodge at Macquarie Park on February 24.

That was before a 50-year-old aged care nurse from the facility tested positive for the coronavirus.

A 95-year-old female resident has since died from the virus and two male residents, aged 82 and 70, are also infected.

Four family members of the deceased woman are being tested to determine if they have contracted the virus.

All visitors have since been banned from the site, with residents confined to their rooms, including at meal times, to prevent any further spread.

Dr Chant also advised aged care facilities to stop hosting children from child care centres to reduce the risk of infection for Australia's most elderly and frail.

One of the two infected male residents wasn't directly cared for by the sick worker, and Dr Chant has warned more cases from the home are expected, with residents continuing to be actively screened for any sign of illness.

So far there's no sign of illness in the children and tests on a staff member who reported respiratory symptoms after the visit have been negative.

On the day the children visited, the aged care nurse with the virus was not present.

But a health clinic will be run on Thursday night to assess the children and reassure their families, Dr Chant said.

Dr Chant said the clinic was being run out of "an abundance of caution" to rule out any link between the children's visit and the nursing home outbreak, noting that children were good at spreading respiratory diseases.

NSW Health Minister Brad Hazzard said it was clear the outbreak had reached a new phase in the state.

"It is fair to say that we do have an evolution happening in the spread of this virus. NSW Health is doing everything they can to try to still contain it, but we do know that containment is ... an unlikely outcome," he said.

He also revealed the two Sydney doctors who have the virus attended the same medical workshop on February 18, alongside about 70 other medical professionals.

The doctors, from Ryde and Liverpool hospitals, are so far the only ones who are sick from that group, and 14 days have passed, giving authorities hope that no one else has been infected.

But the group of doctors and health professionals is being monitored for any further signs of illness although authorities have been unable to contact 10 attendees despite multiple calls and messages.

Mr Hazzard said members of the public, and even some staff, had expressed concerns that it was no longer safe to attend Ryde Hospital.

But the minister said every possible step had been taken to ensure the facility did not pose a public health risk.

Australian Associated Press