The news has raised hopes authorities may have managed to contain an outbreak in Sydney's northern beachside suburbs, where 250,000 people are on day three off a five day locked down.

15 new cases were reported on Monday compared to 36 the day before.

But more than 80 locations, including cafes and gyms across Sydney, were identified as having been visited by people who have since tested positive.

New South Wales Premier Gladys Burrage, Italy in the restrictions may need to stay in place for Christmas.

We need to monitor and make a final call on Wednesday as to what Christmas on the next few days will look like and I appreciate people have plans in place.

I mean, my family is no different to anybody else's.

We're all I think we all empathize with each other.

The government also confirmed it had detected cases in return to UK travelers off the fast spreading new coronavirus strain found in Britain, but that the Sydney cluster strain did not have the mutations.

The original source of that cluster is still unknown, but tests show the strain is almost identical to the one found in a woman who arrived in Sydney from the United States earlier this month.

Meanwhile, other Australian states and territories have moved quickly to close their borders toe all of Sydney's five million residents.

Dozens of domestic flights due to leave the city on Monday were canceled, and states have begun operating checkpoints along the border with New South Wales.