One of the new cases is a woman in her 30s who is related to a deceased resident from the Dorothy Henderson Lodge aged care facility, NSW Health said. Four of the other cases were people who had recently arrived in NSW from overseas. They are a woman in her 50s who had arrived in NSW from the US; a man in his 50s who had also recently arrived from the US, but who was unrelated to the first US case; a man in his 60s who had recently arrived from Switzerland; and a woman in her 60s who had recently arrived from Italy and is linked to a previously infected person. Loading Replay Replay video Play video Play video NSW Health said the sixth case was a woman in her 40s whose case remained under investigation. Health security expert Adam Kamradt-Scott said while it was possible that the virus would "disseminate widely" across the city, it's more likely new cases will be concentrated in some areas.

"The outbreak in Australia is unfolding just like we'd expect, we've seen imported cases initially and where imported cases slipped through the net of our surveillance system, we've then seen small clusters of cases emerge," Associate Professor Kamradt-Scott, from the University of Sydney, said. The state's first four confirmed cases in late January had all recently travelled to China but, following the implementation of a travel ban and mandatory quarantine period for people returning from the country in February, no other cases have had a known history of recent travel there. There were no new cases in February but of the new cases in NSW in March, seven had recently returned from Iran, four from Italy, two from the US, one from Switzerland, and six had travelled to Japan, the Philippines, Singapore or South Korea. However, since Friday, the number of cases being confirmed each day with no history of international travel has exceeded the number of imported cases for the first time since the outbreak in NSW.

By Tuesday, only 25 of the 61 confirmed cases had recently travelled to another country. While there have been an average of nearly six new cases every day this month in NSW, Associate Professor Kamradt-Scott said there was "no guarantee" that the number of confirmed cases would continue to increase at the same rate. "This is not inevitable," he said. The number of COVID-19 cases in Sydney jumped to 61 on Tuesday, with the biggest cluster in the city's north-west. Credit:Louise Kennerley Associate Professor Kamradt-Scott said public health measures, including a shutdown of schools and childcare centres, and "social distances measures", such as putting up signs on public transport to tell people to stay at least one metre apart from each other, could help contain the virus.

"There is a variety of different measures that governments will be considering, but we're not there yet," he said. NSW Health said it "is continuing to find and respond to cases as they are diagnosed to slow any spread of COVID-19 in the community". In a statement on Tuesday night, NSW Health said one person previously confirmed to have COVID-19 had attended St Leonards TAFE on two days while potentially infectious. "Although it has been more than 14 days since the last day of attendance by the confirmed case, NSW Health has been contacting all other students and teachers in these classes, with the assistance of TAFE NSW," the statement said. "We have contacted 20 of the 21 contacts and all report being well with no one having had a respiratory illness. The last student has been contacted via email and phone messages. NSW Public Health officers will be continue to follow up with this last person."

Loading So far, the highest number of NSW cases, 14, have been in people aged between 50 and 59, followed by 12 in people aged between 40 and 49 and nine in those aged between 30 and 39. The majority of cases have had mild to moderate symptoms. However, the oldest two cases, aged 82 and 94, both residents of the Dorothy Henderson Lodge, have died. A 78-year-old from Western Australia was the other COVID-19 death in Australia. The first four cases of the virus, confirmed in late January, were all discharged from hospital by February 13.