"It's good fortune that we haven't had an outbreak in a highly-connected group, it's all about the ability of contact tracers to get to each [potentially infected] person within three days to ensure they can get isolated and stay in isolation," Professor McLaws said.

"In Victoria, looking at case sources, it stemmed from an outbreak in a quarantine hotel, that then moved into large family clusters living in crowded conditions in public housing and with a high degree of connectivity to other people.

"At the same time, they had case numbers in aged care facilities going up and they've had occupational acquisition in meat works facilities where people work long shifts in close confinement and often travel to and from work together."

But Professor McLaws said the situation in NSW could still get out of hand.

"There's still the potential that this could get out of control in NSW, there are 20 per cent to 30 per cent of people who are asymptomatic and won't come forward for testing until the contact tracers get to them," she said.

A spokesman for NSW Health said the contact tracing team has scaled up to 300 staff in the past two weeks and has contacted 4985 people in the past seven days.

"In addition, NSW is supporting Victoria's overall COVID response, exploring ways to provide further contact-tracing support," the spokesman said.

Lyn Gilbert, a professor and senior researcher at the Marie Bashir Institute for Infectious Diseases and Biosecurity at the University of Sydney, said there was more awareness of the possibility of a second wave in NSW, which started recording double-digit case numbers about a month after Victoria, as well as a different pattern of spread.

"In Victoria, there was clearly some sort of breach of quarantine and it had spread and got a bit out of control before it was recognised," Professor Gilbert said.

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"In NSW we knew there was a problem in Victoria, there was a heightened awareness of the risk.

"In both cases there has been widespread testing but in NSW, we haven't seen spread through large family gatherings, which have the highest risk of transmission."

Professor McLaws said each person confirmed with COVID-19 generally has between 10 and 20 contacts that health authorities need to speak to.

With less than 20 new cases being recorded in NSW every day, contact tracers would be trying to track down at least 150 to 300 people every day.

"That's still a lot to deal with but it's just manageable," she said.

In comparison, by day 15 in Victoria, there were up to 70 new cases being recorded every day, requiring contact tracers to speak to as many as 1400 people daily to keep up with the virus.

Victoria reported 532 new cases on Monday, 384 on Tuesday and 295 on Wednesday.

"That's an awful lot of people to find, you can't do that over a 14-day period successfully without having to ring people up at midnight," Professor McLaws said.