Tasmania has reneged on its agreement to open its border to South Australia, Western Australia and the Northern Territory at the end of the week.
The Apple Isle, which is currently coronavirus-free, was set to open its border to SA, WA and NT on 7 August, followed by Queensland, NSW and the ACT on 14 August.
However, Tasmanian Premier Peter Gutwein on Monday said his government would not open the state to anyone until at least 31 August.
Health authorities would review figures on the mainland on a week-by-week basis.
It comes as Victoria declares a state of disaster and imposes a 8pm-5am curfew in Melbourne, with hundreds of new COVID-19 cases recorded each day.
"It simply isn't the time to open the borders right now," Mr Gutwein said. "Now is the time to utilise our best asset, which is our moat."
Tasmania recorded no COVID-19 cases from about 800 tests on Sunday.
The Tasmanian government's decision to continue mandatory 14-day hotel quarantine periods for arrivals follows a decision on Friday to ban travellers from COVID-19 hotspots in Queensland, with virus-hit regions of NSW and Victoria already banned.
People from those areas are only allowed in under exceptional circumstances.
Mr Gutwein implored people to do the right thing when filling out border documents.
Tasmania regained its virus-free status after the recovery of a young woman who returned from Victoria and tested positive while in hotel quarantine on 20 July.
Some business groups had called for borders to stay closed and internal restrictions to be further eased, considering the island state is virus-free.
People in Australia must stay at least 1.5 metres away from others. Check your state’s restrictions on gathering limits.
If you are experiencing cold or flu symptoms, stay home and arrange a test by calling your doctor or contact the Coronavirus Health Information Hotline on 1800 020 080.
