NSW residents have been urged to limit their activity and wear a mask in public if social distancing can't be guaranteed as COVID-19 cases across the state continue to rise.
Premier Gladys Berejiklian said on Monday she was incredibly concerned that NSW was at a critical point in the pandemic.
She said the state has the chance to get ahead of the virus and control the spread if residents limit their activities and practise social distancing over the next few weeks.
"If you cannot guarantee social distancing where you're going ... you must wear a mask," she told reporters in Sydney.
"We encourage everybody to limit their behaviour or activity in the next few weeks especially around large crowds."
The premier noted it was positive that all the new cases reported on Monday were from known sources but urged people to consider avoiding crowds.
The state recorded 20 new COVID-19 cases in the 24 hours to 8pm on Sunday which is the highest number of new cases recorded in three months.
Three of the cases are linked to the Crossroads Hotel in Casula, bringing the total number of cases linked to the cluster to 48.
Eight new cases are linked to the Thai Rock restaurant in Wetherill Park, four are linked to the Batemans Bay Soldiers Club, four are returned travellers in hotel quarantine and one is a person who has returned from Victoria.
Eight cases in all are linked to the Batemans Bay Soldiers Club, while a total of 16 cases are connected to the Thai Rock.
Bega MP Andrew Constance, whose electorate covers Batemans Bay, said people are concerned given "a couple of hundred" people visit the Batemans Bay Soldiers Club every night.
Anyone who visited the club between July 13 and July 17 July needs to self-isolate with Mr Constance warning if they don't, "we're in trouble".
NSW Health on Monday afternoon directed anyone who attended the Our Lady of Lebanon Cathedral in Harris Park between July 15 to 17 to self-isolate for 14 days and come forward for testing even if they're not experiencing symptoms.
The alert was issued after authorities discovered a confirmed COVID-19 case linked to the Thai Rock restaurant cluster visited the church four times before being diagnosed.
Two additional people who attended services between those dates have also tested positive to coronavirus. These cases were not included in Monday's confirmed numbers.
From midnight on Tuesday, NSW will enforce tougher border restrictions for people wanting to enter from Victoria.
A border zone will be set up along the Murray River and all current travel permits will be cancelled while residents in the border zone who wish to move between the states will have to reapply.
Travel will only be allowed for work, education, medical care, supplies or health services.
Among the changed permit requirements, staff or students of boarding schools or universities must self-isolate for two weeks and obtain a negative swab before attending school.
If NSW residents travel into Victoria, they will have to self-isolate for two weeks when they return.
Victoria recorded 275 new coronavirus cases on Monday, and masks are to be mandatory for people in living in metropolitan Melbourne and the Mitchell Shire from Thursday.
Victorian Premier Daniel Andrews on Monday said he understands Ms Berejikian's decision to tighten the border restrictions.
Meanwhile, Sutherland Local Court has been closed for cleaning after a person who attended last Wednesday tested positive for COVID.19.