Tasmania's premier has made no apologies for swiftly shutting borders with parts of Western Australia after one COVID-19 case in Perth.
Travellers from Perth and the Peel and South West regions are not allowed to enter the island state unless granted special permission as an essential worker.
The move was announced late on Sunday night after a Perth hotel quarantine worker tested positive.
Anyone in Tasmania who has been at the high risk regions since January 25 has been told to immediately self-isolate and contact public health.
There are 789 people who have arrived in Tasmania from WA since January 25.
Tasmanian residents who have been in the WA high-risk areas are allowed to return home but must quarantine for two weeks.
"This is obviously a challenging period. On the weekend we declared we were open to the rest of the country," Premier Peter Gutwein said on Monday.
"My understanding is, with the circumstances in WA, that lasted for 21 hours.
"I am sorry for the disruption but I make no apologies in terms of ensuring that we manage things and ... keep our community safe."
The WA government has placed Perth and the Peel and South West regions into a five-day lockdown.
Tasmania remains open to the rest of Australia, after dropping border restrictions with ten Greater Sydney regions on Sunday.