COVID-19 restrictions in Sydney will likely be extended as an outbreak in the city reaches a "critical phase".
Two new locally transmitted cases have been recorded in NSW, taking Sydney's eastern suburbs COVID cluster to 11.
Chief Health Officer Kerry Chant says it's an "optimistic sign" the pair are both close contacts of previously reported cases and tested positive while in isolation.
The woman in her 50s from Sydney's north and the man in his 30s from the eastern suburbs were both diagnosed after the 8pm cut off and will be included in Tuesday's numbers.
Another two cases, announced on Sunday morning, were recorded in the 24 hours to 8pm on Sunday and have been included in Monday's figures.
NSW Premier Gladys Berejiklian says authorities are very concerned by the extremely contagious nature of this Delta strain.
"In some instances, the exchanges have been scaringly fleeting," she told reporters on Monday.
"People not even physically touching each other but literally fleetingly coming into the same airspace has seen the virus transferred from one person to another."
Dr Chant says the new infections are a positive sign contact tracing and isolation is working, but says NSW isn't out of the woods.
"From one person alone we've had four or five cases ... even if they infect one or two each, you can see how it grows exponentially."
"That's why this is such a critical phase.
"We need to find all the cases, and make sure we identify the close contacts and casual contacts."
NSW Health said in a statement that people in the eastern suburbs who don't have symptoms and have not been at exposure venues at the listed times don't need to isolate.
However they are encouraged to avoid gatherings, minimise their movements, and work from home if possible.
The growing cluster has also prompted the government to mandate mask-wearing in seven local council areas.
Anyone shopping, working in hospitality or indoors must wear a mask unless eating or drinking if they live in the local government areas of Randwick, Bayside, Botany Bay, Inner West, City of Sydney, Waverley and Woollahra.
Masks are also compulsory on public transport in Greater Sydney, Wollongong and Shellharbour local government areas until Thursday.
Greater Sydney and Blue Mountains residents have been told to avoid non-essential visits to aged care and disability facilities and if visiting must wear a mask with a limit of two visitors a day.
Ms Berejiklian said restrictions would likely be extended and called for more people to get tested.
She also appealed for more Pfizer vaccine doses at a national cabinet meeting on Monday.
"The current outbreak we're experiencing demonstrates the risk is always there, the threats are always there, no matter how good your systems are," Ms Berejiklian told Sydney radio 2GB on Monday morning.
"Other states have received a top-up, and I just want to make sure we get our fair share, especially given the vast majority of Aussies coming back home are coming through Sydney Airport."
She later told reporters she had been assured the doses would be distributed to states according to their population.
The latest outbreak was sparked last week when an unvaccinated limousine driver, who transported overseas aircrew to and from the airport, tested positive after visiting multiple venues, including the popular Bondi Junction shopping centre.
Hundreds of people are isolating after scores of close contact exposure sites were identified across more than a dozen suburbs.
Australian Associated Press