Tasmania's public health authorities are expected to declare the ACT a high-risk zone from 5pm on Thursday.
The decision will follow one made by the ACT Government earlier in the day to enter a snap lockdown from that time for the next seven days.
Declaration of the jurisdiction as a high-risk zone means anyone who has spent time in the ACT will not be able to enter Tasmania unless they are an authorised essential traveller.
If they are approved to enter the state, they will be required to spent 14 days in quarantine at a suitable premises.
Anyone in Tasmania who has recently spent time in the ACT is asked to monitor their symptoms.
If COVID-19 symptoms emerge, no matter how mild, they are asked to self-isolate and contact the Public Health hotline to organise a test.