NSW Health has confirmed a 95-year-old woman who died at a Sydney nursing home tested positive for coronavirus.

Key points: The dead woman had contact with an aged-care worker who contracted coronavirus despite not travelling overseas

The dead woman had contact with an aged-care worker who contracted coronavirus despite not travelling overseas There have now been 22 confirmed cases in the state

There have now been 22 confirmed cases in the state NSW Premier Gladys Berejiklian described the number of infections as "a concern"

Last night the health department confirmed five more cases in the state, bringing the number of infections in NSW since the COVID-19 outbreak began to 22.

The 95-year-old resident at the Dorothy Henderson Lounge in Macquarie Park, in Sydney's north, died on Tuesday in hospital. Another elderly resident at the facility also tested positive for the virus.

An aged-care worker at the facility was diagnosed with coronavirus earlier this week, becoming the third person to be infected via human-to-human transmission in Australia.

NSW chief medical officer Dr Kerry Chant said the five new cases also included a female doctor who worked at Liverpool Hospital, and a female on the Northern Beaches.

"The female doctor who was diagnosed on March 4 had no history of overseas travel," she said.

"We are immediately establishing which staff and patients may need to self-isolate and be tested for COVID-19 should they be unwell."

A 50-year-old man from Cronulla and a 60-year-old woman, who is believed to have returned from the Philippines, also tested positive.

Her travel details are being obtained and will be disclosed if it is decided that she posed a risk to any other passengers on her flight.

Eleven of the residents at Dorothy Henderson Lodge are now in isolation. ( ABC News: Liv Casben )

NSW Health Minister Brad Hazzard said the aged-care worker had contact with 13 residents of the Macquarie Park home, and that two of them, including the woman who died, subsequently reported respiratory symptoms.

The other affected resident is an 82-year-old man who is being treated in hospital after testing positive on Tuesday.

It is unclear how the worker contracted coronavirus, as she had not been overseas.

She is now in a stable condition at Royal North Shore Hospital.

"It is concerning when we have someone present with coronavirus and we can't track the source," Mr Hazzard said.

"[NSW] Health is looking at how we can step up some of the testing that goes on with some of the people who present with respiratory symptoms that in the normal course may not have been considered for coronavirus testing."

Dr Chant rejected the suggestion the Macquarie Park facility needed to be in full lockdown and said infection control staff visited last night.

She said it was pleasing to note that the centre had already taken a "lot of steps" to raise infection control.

A 53-year-old doctor working at Sydney's Ryde Hospital tested positive after treating patients with coronavirus, while another woman contracted COVID-19 from a relative who had travelled to Iran.

Thirteen doctors, 23 nurses and four other health workers are in home isolation after interacting with the doctor.

Several planes infected

Meanwhile, health authorities are scrambling to contact people who travelled on flights to Sydney with people who had the virus.

Overnight, a man in his 30s tested positive for coronavirus after he travelled to Australia from Iran via Malaysia and Singapore at the weekend.

He was on Jetstar Asia flight 3K686 from Kuala Lumpur to Singapore on February 29, and then Qantas flight QF82 to Sydney, arriving on March 1.

NSW Health warned he may have been infectious while on the plane and said it would contact passengers seated around him.

He remains in isolation at Westmead Hospital in Western Sydney.

The man is a lecturer in the science and engineering faculty at Macquarie University but had not been on campus nor had contact with staff or students since his return from Iran.

In a statement, the university said: "There is no evidence to suggest that the aged-care worker from Baptist Aged Care who has contracted COVID-19 has done so as a result of contact with a member of the Macquarie University community."

There are several other flights to the Harbour City that had infected passengers on them, including:

Qantas flight QF02 from Singapore on February 28

Qantas flight QF02 from Singapore on February 28 Korean Air flight KE121 from Seoul on February 27

Korean Air flight KE121 from Seoul on February 27 Malindo Air flight OD171 from Kuala Lumpur, arriving on March 1

Health authorities have asked people travelling from Iran, South Korea and Japan to be particularly vigilant for COVID-19 symptoms including a sore throat, fatigue and coughing.

"There has been a rapid increase in COVID-19 activity there in recent days," a NSW Health spokesperson said.

NSW Health said Iran was among three countries worst-affected in the surge of coronavirus over the past few days. ( AP: Vahid Salemi )

NSW Premier Gladys Berejiklian advised people to "stay calm", despite the spike in numbers.

"Yes it is a concern and all of us should be cautious, all of us should take the advice of health experts, no doubt about it — but we should also go about our business and not panic," she said.

Australia's chief medical officer, Professor Brendan Murphy, told Senate estimates that 80 per cent of people who contract coronavirus exhibit "such mild symptoms they barely notice it and that's particularly the case in children".

"But there is no doubt that there is a mortality," he qualified.

An expert in infectious diseases said it was concerning health authorities did not know how the disease had spread locally.

Professor of Biosecurity at the University of NSW, Raina MacIntyre, said it might indicate people were presenting to hospital with a fever but while being unknowingly infected with coronavirus.

Italian authorities reported a spike in coronavirus deaths overnight, with 27 fatalities increasing the total death toll in the country to 79.