Under the updated public health direction all non-ACT residents who have been in the northern beaches of Sydney, Greater Sydney or the Central Coast or Wollongong areas of NSW, and do not have a valid exemption, will be refused entry to the ACT.

If people from these areas need to travel to the ACT for extraordinary circumstances, they will need to apply for an exemption at least three days before their travel.

The changes apply to non-ACT residents only and do not change the current travel requirements for ACT residents returning from COVID-19 affected areas.

ACT Chief Health Officer Kerryn Coleman said about 2,000 people were currently in quarantine in Canberra, 25 per cent of whom were non-ACT residents.

"We are putting in place strengthened travel restrictions to make it absolutely clear to non-ACT residents who live in or have recently visited COVID-19 affected areas of NSW that they are not able to be in the ACT at this time," Dr Coleman said.

"For those in COVID-19 affected areas of NSW, we ask that you respect the public health direction that has been put in place and do not travel to the ACT."

ACT Health will work with accommodation providers to ensure they are aware of the requirements for travellers from COVID-19 affected areas of NSW to have an exemption, the ACT Government said, while police will "have a presence" at the Federal Highway beore the midday deadline.

The ACT is the latest jurisdiction to strengthen border controls in light of the NSW clusters, with Victoria's hard border closure coming into effect overnight.

NSW records three new COVID-19 cases in western Sydney, no links to northern beaches cluster

NSW has recorded three new cases of COVID-19 in Western Sydney following a subdued New Years Eve in the Harbour City.

Two men, one in his 40s and one in his 20s, have tested positive and a third man, also in his 20s, is a close household contact of one of those cases.

None of the cases are linked to the northern beaches cluster and investigations are ongoing, chief health officer Kerry Chant said.

NSW Premier Gladys Berejiklian has asked anyone living in the western Sydney suburbs of Greystanes, Auburn, Lidcombe and Berala to be on high alert for symptoms.

Several heath alerts have been issued by NSW Health about venues in these suburbs, including BWS Berala, Bunnings Lidcombe.

"Those cases in western Sydney are a big concern for us but we are deeply grateful that everybody who has been identified as positive has been really cooperative, they have spent hours on the phones to our experts," Ms Berejiklian said.

Genomic sequencing has also now revealed the Croydon cluster in Sydney's inner west and the two cases in Wollongong are linked to the Avalon cluster on the northern beaches.

Dr Chant said a case from Croydon and another case from Wollongong both attended the Swallowed Anchor restaurant in Wollongong on December 19.

She called for anyone at the restaurant on that date to immediately get tested and self-isolate.

"I want to acknowledge the person who actually just made that link," she said.

"So what we're looking at is who else was at that restaurant who could have been exposed them both at that time.

"It may turn out that that is a furphy but clearly it is an interesting link and given the movements, it would have to be a very amazing coincidence if it wasn't linked."

The Croydon cluster is made up of nine extended family members and the Avalon cluster now stands at 146 cases.

Health authorities have also discovered two positive cases from Victoria recently travelled to the NSW south coast.

The pair visited the the Great Southern Hotel in Eden on December 30 and Bermi's Beachside Café in Bermagui on December 31.

Contact tracing is underway for both venues.

"It is important that if you know anybody within the Bermagui area that you reach out to them and make sure that they are aware of this," Dr Chant said.

"We understand that there may be a lot of visitors who have travelled to that part over the festive season."

Across the state of NSW there were 32,000 COVID-19 tests conducted in the past 24 hours.