This catchment serves a population of 32,000 people and takes sewage from Narrawallee, Milton, Mollymook Beach, Ulladulla, Kings Point, Burrill Lake, Dolphin Point, Lake Tabourie.

There have been no recent locally acquired cases or returned travellers who tested positive from this area.

However NSW Chief Health Officer Dr Kerry Chant said it could mean there are undetected cases of COVID in the community - or that someone with the virus visited the area.

Everyone in the area is being urged to be especially vigilant in monitoring for symptoms, and if they appear get tested and isolate immediately.

"This is a time of year where we have lots of mobility so we can't exclude that someone who has cleared the infection in either NSW, Victoria or a returned traveller from interstate may have visited the area," Dr Chant said.

"But we do need the community to respond, and also if anyone has recently been in that area please also come out for testing."

It comes as NSW recorded four new locally acquired cases of COVID-19 in the 24 hours to 8pm last night.

One of these cases, a man from the northern zone of the Northern Beaches first reported yesterday but included in today's numbers, remains under investigation.

Another is linked to the Croydon cluster, and is a close contact of a previously reported case. There are now 11 cases in this cluster.

And two cases are linked to the Berala cluster, and are close contacts of previously reported cases, which brings the total number of cases in this cluster to 20 .

Seven cases were also recorded in returned travellers, bringing the total number of cases in NSW since the beginning of the pandemic to 4806.

There were 26,112 tests reported to 8pm last night, compared with the previous day's total of 27,879.

NSW Health continues to urge everyone throughout the state to continue to come forward with even the mildest of symptoms

Across the border, Greater Brisbane will enter a hard lockdown from 6pm on Friday after a cleaner at a quarantine hotel was diagnosed with the highly contagious UK strain of COVID-19.

Residents in the council areas of Brisbane, Logan, Ipswich, Moreton Bay and Redlands will be required to stay at home until 6pm Monday except for essential work, exercise, essential shopping and to access healthcare or to look after the vulnerable.

The Service NSW app, which hosts a mandatory check-in system for hospitality venues, stopped working for several hours on Thursday afternoon.

It has been compulsory to use the app in some businesses since the start of 2021.

Meanwhile, the second day of the Australia-India Test will be played at the SCG on Friday, with all attendees forced to wear masks except when eating or drinking.

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