The most likely "ground zero" of an outbreak of coronavirus at the North West Regional Hospital was the Ruby Princess cruise ship, a new report has found.
An interim report into the outbreak was released on Thursday morning.
Public Health director Mark Veitch said the document was a descriptive epidemiological account of the outbreak comprised of information about each case related to the cluster.
"These sort of reports take a higher-level look at the event but nevertheless seek to prevent and address future outbreaks," Dr Veitch said.
"The focus is the who, where, when of cases ... and it looks to find things in common with cases to explain how the outbreak occurred."
Dr Veitch said two cruise ship related cases of COVID-19 were admitted to the NWRH in late March and the first staff member became sick on April 3.
"Our impression was the cruise ship related cases had given rise to infection in one or more health care workers and there was subsequent transmission to other health care workers," he said.
Dr Veitch said it was likely by the time cases were diagnosed there was already established person-to-person transmission of coronavirus within the hospital.
Premier Peter Gutwein said the Ruby Princess was responsible for about one in 10 of Australia's coronavirus cases.
"Most likely the Ruby Princess is the root cause of our problems on the North-West Coast. In terms of how this disease has spread is frankly something we will never know," Mr Gutwein said.
The Premier said he wanted to make it clear no passenger or health care worker was to blame.
"Don't use this report to blame people. Use this report to learn and to go forward," Mr Gutwein said.
Health Minister Sarah Courtney said the report made it clear COVID-19 was a disease which had never been seen before.
"What this report makes clear is the government took strong action at key times," Ms Courtney said.
Ms Courtney said she had accepted all of the report's recommendations.
She said some recommendations could be implemented quickly and others had already been implemented.
Meanwhile, Tasmania's COVID-19 death toll has risen to 12 with the death of an 86-year-old North-West woman on Wednesday.
Mr Gutwein expressed his condolences to the woman's loved ones.
"We've now tragically lost 12 lives to coronavirus in Tasmania, 11 of those in the North of the state," Mr Gutwein said.
There have been 219 cases of coronavirus in the state of which 144 people have now recovered.