About one-third of COVID testing occurring in Tasmania is coming back positive - one of the highest rates in Australia.

Director of Public Health Mark Veitch said cases would continue to rise during mid-to-late January before reaching a peak, but it was too early to say when that peak could occur. The government estimates more than 2000 cases could be detected per day.

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Almost 60 per cent of cases are aged between 20 and 39, and 85 per cent are aged under 50.

Dr Veitch said it would get to a stage where gatherings of people would need to assume at least someone was COVID-positive.

"It's very likely that in the course of this first wave, a very high proportion of people in that young adult age group will become infected with the Omicron strain of COVID," he said.

"At the moment, around about one-in-170 Tasmanians is a diagnosed active case.

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"And I would not at all be surprised in a weeks' time as many as one-in-50 Tasmanians are on the list as a current, active case of COVID.

"That tells us something quite important. It tells us that COVID is very widespread, it also means that wherever you go in a gathering of a few dozen people, it's quite likely that over the coming weeks there'll be someone in that group who has COVID."

When asked about COVID spreading undetected in the community - above rates discovered through testing - Dr Veitch said this was likely, but he said symptomatic cases were more likely to be infectious than asymptomatic.

Five COVID-positive people are in hospital in Tasmania, but none are being treated for COVID due to their hospitalisation occurring for other medical reasons.

Dr Veitch said about one-in-100 cases would require hospitalisation, and 10 per cent of those could end up in intensive care.

"That means roughly one-in-1000 cases could end up in intensive care," he said.

Dr Veitch said deaths were expected in the coming months, but that between 50 and 100 Tasmanians typically die from influenza each year.

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Tasmania has 3118 active cases of COVID after recording a further 867 on Wednesday morning.

Based on interstate and international evidence, waves of COVID can last between one and three months, Dr Veitch said.

Fifteen aged care facilities in Tasmania have now recorded a positive COVID case.

Of those, 13 involved an individual worker who has been infected.

Two have seen some spread of COVID.

The government will no longer list exposure sites due to them becoming "extremely numerous".

Dr Veitch said the approach would change to relying on Tasmanians to be "vigilant" when in a public place.

"We are not going to continue to list public exposure sites because it's absolutely important that the public understands that wherever you go in Tasmania over the coming weeks during this peak of the Omicron outbreak, that there's a very good chance that you're somewhere where there's someone with COVID," he said.

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"Simply listing the places that we know where a case has gone doesn't mention all the other places where people with COVID have probably been.

"It means you have to be vigilant. It means you need to wear masks in public places, and to be aware that symptoms that you get in the coming weeks of a respiratory illness could be COVID."

Several Facebook groups have started - some with up to 25,000 members - to list known exposure sites.

The risk posed by international arrivals has been downgraded to the same level as interstate arrivals, Premier Peter Gutwein said.

This means from midnight tonight, they are not required to undertake isolation, but must get tested if they develop symptoms.

Arrivals are also subject to vaccination and pre-testing requirements, with more information on the coronavirus.tas.gov.au website.

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