The operator of a western Sydney aged care home where 12 residents with COVID-19 have died expects more fatalities in the coming days, with the facility running as a "pseudo" hospital in an attempt to manage the outbreak.

The Anglicare-run Newmarch House reported five deaths in just over 24 hours this week, with chief executive Grant Millard saying the facility had been warned to expect difficult days ahead.

The latest COVID-19 death at the facility - the 12th overall - was confirmed on Wednesday afternoon.

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Mary Watson, whose 93-year-old mother is a resident in Newmarch nursing home, said she was "flabbergasted" by the situation.

“The problems we still face is the lack of communication and transparency from Anglicare," she said.

Ms Watson said she hoped her recent discussion with Anglicare chief executive Grant Millard would improve the situation for her mother.

“He has assured me these changes will be occurring now but eleven people have already passed,” she said.

“I’m just flabbergasted that it has taken all of this to get action and care for our parents inside.”

Mr Millard said the situation was one of "significant and deep trauma".

"We do anticipate more deaths," he told ABC News on Wednesday.

Some 20 registered nurses, 25 carers, 11 cleaners and a GP are working daily at the nursing home, where 34 residents and 22 staff members have tested positive to COVID-19.

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"(It's) really running as a pseudo of a hospital at the moment," Mr Millard said.

Residents have been isolating in their homes since the outbreak on 11 April, with Anglicare working to connect them with family members via mobile phones.

The federal government's deputy chief medical officer Paul Kelly said there were important lessons to learn from the outbreak.

"It's certainly not a blame game and the circumstances of that particular case will come out in time," he told reporters on Wednesday.

"Even the most mild symptoms can be quite infectious, as we've found in this case when we're dealing with vulnerable people."

A registered nurse also makes daily calls to each infected resident's designated family representative, Mr Millard said.

Other employees have been tasked with helping residents who cannot use mobile phones to connect with their family, with Mr Millard saying it's "sincerely regrettable" those calls have not been happening frequently enough.

"You need to appreciate that some people you are bringing in for these services are not clinicians, they're not used to wearing personal protective equipment," he told ABC News.

"It's a very dangerous place for people to be working."

The facility is looking into window therapy, in which residents can communicate with family members and receive therapy through a window.

NSW Premier Gladys Berejiklian on Wednesday said it was "distressing" communication between family members of Newmarch House residents and operators Anglicare was lax.

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An open letter from families of the facility's residents to Mr Millard claims their calls have not been returned, details about loved ones have not been regularly divulged and residents have reported inadequate care.

The premier said the lack of communication was a "huge issue" given the fear and distress felt by family members and residents of the home.

"We say to the operators of that aged care home, you need to lift your game in communicating to loved ones," Ms Berejiklian told reporters on Wednesday.

"It's not acceptable to keep people in the dark. Just put yourself in the shoes of those people - it's horrific to be fearful about, firstly, potentially losing a loved one, but then not knowing what's going on and not being able to offer that care."

Infectious disease clinicians are assessing the situation at the facility daily, while staff who helped manage a coronavirus outbreak at Dorothy Henderson Lodge aged care home in Macquarie Park have also been called in to help.

NSW chief health officer Dr Kerry Chant said a report on the Newmarch House outbreak will be prepared and shared with families before its findings are made public.

Anglicare said the virus was introduced to the Caddens facility by an employee who worked for six consecutive days while suffering very mild respiratory symptoms.

Federal Aged Care Minister Richard Colbeck says a teleconference call of medical experts is expected to be held on Wednesday to discuss further action.

People in Australia must stay at least 1.5 metres away from others and gatherings are limited to two people unless you are with your family or household.

If you believe you may have contracted the virus, call your doctor (don’t visit) or contact the national Coronavirus Health Information Hotline on 1800 020 080. If you are struggling to breathe or experiencing a medical emergency, call 000.

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