Tasmania has shut its border with South Australia in response to a growing coronavirus outbreak in the mainland state.
The directive was implemented at 4pm on Tuesday.
It means no one from South Australia can enter Tasmania unless approved as an essential traveller.
Anyone in Tasmania who has been in South Australia since July 8 is encouraged to check the health department's list of high-risk premises and immediately isolate if they've been to any of the venues.
South Australia is implementing a seven-day lockdown from 6pm on Tuesday after a cluster of local COVID-19 cases grew to five.
"Our thoughts are with those in NSW, Victoria and now South Australia," Tasmanian Premier Peter Gutwein said.
People in Tasmania who have been in South Australia since July 8 are required to wear a mask in public for 14 days since they left the mainland state.
More than 3000 people have arrived in Tasmania from South Australia since July 8.
Tasmania has a hard border in place with Victoria and NSW and has also declared a host of high-risk premises in Queensland.
Mr Gutwein said the travel ban with Victoria would remain in place for at least as long as the mainland state's lockdown, which was on Tuesday extended for a week.
Recent arrivals from Victoria have also been told to wear a mask in public until at least Friday.
Students and staff who have recently been in South Australia, Victoria or NSW have been told to stay home from school until the end of the week.
Australian Associated Press