Tasmania has declared 12 NSW sites and additional Victoria venues high risk after new coronavirus cases in both mainland states.
A returned traveller in NSW recently tested positive after completing their two-week quarantine period.
Health alerts have been issued for locations they visited included a cafe at Brighton Le Sands in southern Sydney as well as shops, a hotel and a beach in the Wollongong area.
The Tasmanian health department on Monday declared the sites high-risk.
Anyone in Tasmania who has been at the locations at certain times since February 2 must self-isolate immediately and contact public health.
People who have visited the venues, including returning Tasmanians, aren't allowed in to the state unless they are granted express permission from the state controller.
Under Tasmanian guidelines, travel from high-risk areas is banned without the special permission.
The island state has also added three venues in Melbourne's west and northwest to the high-risk list after they were visited by a hotel quarantine worker who tested positive on Sunday.
The same self-isolation rules and travel ban applies.
Fourteen premises in Victoria linked to an earlier case remain designated as high risk.
People are urged to check Tasmania's coronavirus website for further information.
The island state dropped its remaining border restrictions with Western Australia at 6pm on Monday, meaning people from Perth and the Peel region no longer have to quarantine.