South Australian Premier Stephen Marshall and the state's chief health officer Nicola Spurrier announced the lockdown today. It will come into effect at midnight tonight.

Two new cases linked to the Parafield cluster in Adelaide's northern suburbs were recorded today, bringing the total number of cases associated with the outbreak to 22.

Mr Gutwein said anyone who had entered Tasmania from South Australia since November 7 would need to continue to self-isolate in a government-run quarantine facility or in a private residence until they'd been in the state for 14 days.

"If you are well and wear a mask, you are also able to leave the state if you have a flight back to South Australia or out of the state," he said.

"Obviously circumstances have changed in South Australia and their government has taken some swift action today.

"We know from our own experience that going early and going hard is the right thing to do."

The Premier asked South Australian arrivals currently in Tasmania to contact the public health hotline if they had been at any one of three premises in Adelaide:

Those who have been at those locations will be asked to quarantine and get tested for coronavirus.

"If you are a family member of someone who has been in one of the premises, we would also ask you to make contact as well as you would be a close contact," Mr Gutwein said.

"My message to South Australians thinking of travelling to Tasmania is: don't come."

The Tasmanian government will continue to classify South Australia as a 'medium-risk' jurisdiction, meaning anyone who arrives in the state from South Australia will have to quarantine in a government facility or a private residence if suitable.

Tasmania's Public Health director Mark Veitch said it was likely that restrictions on South Australian arrivals would remain in place for "another six or seven days".

He also said the likelihood of people in Tasmania having been at either the Lyell McEwin Hostpital, The Aquadome or Woodville Pizza Bar in the specified timeframes was low.

The South Australian outbreak has been traced to a single family and has touched one of the state's quarantine hotels, as well as the aged care sector.

Meanwhile, Australia's acting chief medical officer Paul Kelly announced this afternoon that it would now be mandatory for all people working in hotel quarantine to get tested for COVID-19 at least once a week.