Victoria's state of disaster declaration and Melbourne's hard lockdown will help secure the border with NSW and curb the spread of coronavirus into the state, Premier Gladys Berejiklian says.
NSW recorded 13 new COVID-19 cases in the 24 hours to 8pm on Sunday - four of which were returned travellers from overseas or Victoria and one with no known source.
Another four cases were announced from the weekend - a 52-year-old woman, her son, daughter-in-law and their baby - who recently returned from Melbourne to Wagga Wagga in the Riverina region and went into self-isolation.
It comes after five million Melburnians spent their first night locked inside with a 8pm-5am curfew and learned of the stage-four restrictions - including a travel limitation of five kilometres from home - which will be enforced until at least September 13.
A state of disaster has also been declared, beefing up Victoria Police powers.
Ms Berejiklian on Monday sympathised with Victorian residents but said the stronger restrictions would help protect NSW from the spread of the virus.
"When Victorians themselves cannot be mobile, it obviously helps our job in reducing people getting across the border. But no matter how tough you are, borders aren't impenetrable, we have to remember that," Ms Berejiklian told reporters.
Criteria for travel between NSW and Victoria was tightened two weeks ago, with movement limited to work, education or medical purposes. NSW residents returning from Victoria are forced into two weeks of self-isolation.
"If we have to do more, we will," Ms Berejiklian said.
In NSW, two Newcastle pubs, a club and a drug court in nearby Toronto have been shut for deep cleaning due to visits from infected Sydney residents
NSW health authorities on Sunday confirmed a case connected to Sydney's 26-strong Potts Point cluster worked at Toronto Drug Court last Monday, while another infected man visited Hotel Jesmond on Wednesday and Wallsend Diggers and Lambton Park Hotel on Thursday.
Patrons at certain times on those dates must now self-isolate for 14 days and get tested.
"This action is vital to limit the spread of the virus," Hunter New England local health district's Dr David Durrheim said in a statement on Monday.
NSW Health on Monday added the Fitness First gym in Rockdale and a Bondi yoga studio - both linked to the Potts Point cluster - to the list of venues attended by COVID-positive people.
The NSW government, meanwhile, is strongly recommending people wear masks in high-risk situations as the state enters what Ms Berejiklian labelled a critical phase.
Ms Berejiklian also revealed she now carries a mask at all times and suggested everyone follow suit for situations where social distancing is impossible.
Public-facing workers, worshippers, people living near community clusters and those in enclosed spaces, such as on public transport or in grocery stores, should wear face masks.
Ms Berejiklian stopped short of making masks compulsory but said elderly people or those suffering underlying health issues should also wear masks.
"As we've been saying for weeks, the health advice is evolving," she said.
Eight COVID-19 patients in NSW are in intensive care, with five on ventilators.
An 83-year-old man connected to the Crossroads Hotel cluster in southwest Sydney died at the weekend, taking the NSW death toll to 52, while there are 3797 active cases and 221 people have died throughout the country.
NSW Police said 16 fines had been issued to individuals over the weekend for non-compliance with coronavirus-related public health orders, including for parties in East Jindabyne and Maroubra and a public gathering in Sydney's CBD.