Victorians have been blocked from travelling to Tasmania and anyone who arrives from the state without an exemption will be turned away at their own cost.
The ban, which comes into place at midnight on Wednesday, also includes people who have been in Victoria in the 14 days before their travel.
"The only exception to that will be Tasmanians returning home," Tasmania Premier Peter Gutwein told reporters.
"If visitors arrive from Victoria without an exemption letter, they will be asked to return home. They will be turned back at their own expense."
It comes amid a coronavirus spike in Melbourne which will force more than five million people in the city into lockdown from Thursday.
Tasmania has gone more than 50 days without recording a COVID-19 case and is free of active cases.
The state is planning to reopen its border to mainland Australia on July 24, but Mr Gutwein said that will now exclude Victoria.
He said Victorians could apply for an exemption on compassionate grounds but they are unlikely to be granted one in the short term.
Businesses are no longer allowed to fly in essential workers from Victoria, unless they can prove the skills don't exist in other states.
"Our aim is to ensure Tasmania doesn't suffer a second wave, like Victoria is now suffering," Mr Gutwein said.
"I want to extend our thoughts and support to the Victorians who are in lockdown at the moment."
Biosecurity officers will be stationed at Tullamarine Airport in Melbourne and the city's Spirit of Tasmania Bass Strait ferry port.
Tasmanians returning from Victoria will no longer be allowed to quarantine at home and must instead spend 14 days at a government facility.
Mr Gutwein said the new measures would be reviewed on an ongoing basis, but the six-week Victorian lockdown would provide some guidance.
Australian Associated Press
