Tasmanian borders could close to New South Wales before Christmas due to the rapidly revolving COVID cluster in the mainland state.
The COVID cluster in Sydney's northern beaches area grew to 28 confirmed cases on Friday.
Public Healh Services deputy director Scott McKeown said it was estimated 1000 people from New South Wales had entered the state since December 11 - within the time of incubation for the virus.
He said it was further estimated 200 people had entered the state from the northern beaches area from that date.
Mr McKeown said Public Health would need to assess where cases arise and under what circumstances if it was to advise a shutdown of the state's border to New South Wales.
"If we see further cases arise that indicate a significant public health risk outside of that area, we'll assess that risk and adjust our advice on the areas that we define as high-risk," he said.
"The circumstances in New South Wales are a timely reminder for us all on the need to remain vigilant and how quickly this pandemic can change."
Premier Peter Gutwein said Tasmanians who planned to return home from high-risk areas would be able to enter the state if they proved residency.
He said they must apply or reapply for entry through the G2G app and quarantine in a suitable residence for 14 days and take a coronavirus test within 48 hours.
If that residence did not satisfy social distancing requirements, they must quarantine in a government-run hotel, Mr Gutwein said.
Tasmania declared the Northern Beaches local government area a high-risk area earlier on Friday morning when the total case number was 18.
The Kirribilli Club, Gannons Park, Forest Rangers Football Club, and Penrith RSL Club were classfied as high-risk premises.
People now in Tasmania who have been in high risk areas from December 11 are required to isolate and contact the Public Health Hotline to arrange a test.
People who have been in high-risk areas in the past 14 days and wish to enter Tasmania will not be able to unless entry is approved by the Deputy State Controller.
Updates on high-risk areas can be found at www.coronavirus.tas.gov.au/travelalert.
The rest of New South Wales remains a low-risk area.