New South Wales has recorded 10 new local cases of Covid-19 as Sydney's latest cluster continues to surge.
Five cases were recorded before the 8pm reporting period while the other five were recorded later and will be officially included in tomorrow's numbers.
There are now 21 infections in the NSW's Covid-19 outbreak.
Sydneysiders have been warned the city is in a "danger period" as officials warn the threat posed by the Delta virus strain shouldn't be underestimated.
'Scary' CCTV footage of Covid spread at mall
Footage of a "scarily fleeting" encounter between two Covid-19 cases at a Sydney shopping centre has NSW health authorities on edge, proving the threat posed by the Delta strain shouldn't be underestimated.
Yesterday's two new cases include a woman in her 50s from Sydney's northern suburbs and a man in his 30s from the eastern suburbs. Both are close contacts of known cases and have been in isolation.
CCTV footage inside Bondi Junction Westfield has demonstrated how quickly the strain can spread.
Chief health officer Dr Kerry Chant said the footage showed the virus transmitting between two people during a "momentary crossover" in the shopping centre.
"We know that there's been three people that have been exposed on both June 12 and June 13," she said yesterday.
"In one, we actually have CCTV footage of the encounter and it is basically a crossover of individuals. They are clearly facing each other but it is literally someone moving across from each other for a moment - close, but momentary.
"In two other cases, we haven't been able to, with CCTV footage, look at the exact same crossover point, but we know they were 20 metres [apart], signing in at different venues at the same time or in that area so we suspect they did cross over."
NSW Premier Gladys Berejiklian described the encounter as "scarily fleeting", saying the pair didn't even physically touch each other, with the virus instead being transferred as they came into "the same airspace".
"That's how contagious it is," she said.
The Delta strain, which is believed to be up to 50 per cent more infectious than other variants, first emerged in India and has since spread to dozens of other countries.
It was discovered in the Australian community for the first time earlier this month in Melbourne, when the city was dealing with its own Covid-19 outbreak.
Genomic sequencing has shown the variant on the loose in Sydney matched "perfectly" with a sequence from the US.
Covid restrictions likely to be extended
As concerns around Sydney's outbreak ramp up, Berejiklian revealed the current restrictions around masks for Greater Sydney, the Blue Mountains, Wollongong and Shellharbour would likely be extended.
The Premier said while yesterday's case numbers weren't a "bad outcome" there was still a level of concern about the way this virus has spread "fleetingly" between some cases.
"Given the situation we are in and given we don't want to see further restrictions imposed more broadly across our city and our state, in all likelihood, the existing settings we have in place will continue beyond the five days," she said.
The list of exposure sites visited by known Covid-19 cases is growing rapidly and now includes suburbs in the west as well as in the Illawarra region.
A number of changes to mask restrictions kicked in at 4pm on Sunday, including the requirement for masks on public transport being extended to include Wollongong and Shellharbour.
Previously this restriction only applied to Greater Sydney and the Blue Mountains, but was extended after a confirmed case spent time in Wollongong.
Berejiklian said these mandates were brought in to help avoid a "superspreader event" that could see cases explode across Sydney and surrounding areas.
Masks are now also mandatory in indoor premises for certain local government areas, including Bayside, Canada Bay, Sydney, Randwick, Inner West, Waverley and Woollahra.
The announcement from Berejiklian follows calls from a top epidemiologist for a snap three-day lockdown in Sydney.
Epidemiologist and World Health Organisation adviser, Professor Mary-Louise McLaws, told ABC radio NSW needs to take this outbreak of the Delta variant "very seriously".
"If the numbers go up any further we should really be thinking about a three-day lockdown," she said yesterday.
McLaws also said masks should be made mandatory in all public areas for Greater Sydney.
Berejiklian has previously refused to rule out bringing in tougher restrictions in order to control the outbreak.
She said the next few days are critical for NSW and any further restrictions "will depend on what cases emerge in the next few days".