There have now been 83 cases in total linked to the cluster on the Northern Beaches area of Sydney.

People living in the area have turned up for COVID-19 testing "in droves", despite some delays and queues at testing facilities.

At her morning press conference, Premier Gladys Berejiklian thanked people for coming forward for a "record day" of testing, with more than 38,000 tests performed across the state on Sunday.

She said it was pleasing to see a downward trend in the number of cases, but this virus was particularly volatile, and contagious, and we needed to remain vigilant.

Ms Berejiklian urged people to wear masks in high risk areas, particularly at indoor settings like shopping centres and grocery stores, places of worship, and on public transport.

"We already know what the high risk areas are," she said.

"Don't think you're immune, this can affect anyone.

"We have to be as vigilant as ever."

Chief health officer Dr Kerry Chant said aged care facilities should not accept visitors until at least Wednesday, when more is known about the situation.

"Don't think this is just an Northern Beaches issue," she said.

"We need people to help us identify undiagnosed cases elsewhere. Anyone with symptoms needs to come forward for testing."

Dr Chant also said some close contacts had been unable to be contacted due to leaving illegible contact details at venues.

Deputy Premier John Barilaro asked Sydney residents to reconsider travel plans to regional NSW.

He urged those people from Sydney already holidaying in regional areas to get tested and isolate.