Tests results provided by health authorities in the UK support the likelihood that a former Launceston General Hospital worker contracted COVID-19 during international travel, rather than in Tasmania.

Tasmanian Public Health authorities had previously maintained there was no evidence the worker, who tested positive for COVID-19 in London two days after they left the state, contracted the virus while in the state.

However, a precautionary approach resulted in a list of potential exposure sites being declared across the state, impacting a number of Launceston businesses.

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In a statement, Public Health Director Dr Mark Veitch thanked all those involved in the response.

"The cooperation of businesses, the Tasmanians who got tested, and the use of Check in TAS [app] all contributed to this response and have provided reassurance that the case was very unlikely to have been infected or infectious while in our state," he said.

"Ongoing high levels of testing and negative waste-water testing also contribute to this reassurance.

"Finally, details of test results provided by UK authorities also support the likelihood that the infection was acquired during international travel into the UK, rather than in Tasmania."

Meanwhile, anyone who has recently returned to Tasmania are urged to check for newly listed high-risk premises in South Australia, Victoria, NSW and Queensland.

Tasmania has declared the whole of South Australia, Victoria and NSW as high-risk areas. A number of premises and transport routes in Queensland have also recently been declared high-risk.

Face masks must be worn by anyone already in Tasmania who has been in Victoria or South Australia on or since July 8, not currently in quarantine, when they are outside their accommodation.

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These people are also asked to limit their movements and time in the community, avoid public gatherings and limit visitors to their home.

The only exemptions are for people under the age of 12, or those with a valid medical reason not to wear a mask.

Dr Veitch said the requirement for mask wearing for people recently in Victoria will be reviewed on Friday.

"People subject to the mask requirement (and who are not in quarantine) are not prevented from continuing their work, as long as they are well, can wear a mask at work, and practice COVID-safe behaviours," he said.

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