Acting deputy commissioner Donna Adams said the 2011-12 reporting period showed a similar gap between the alleged assault and the time it was reported, with some cases dating back to the 1950s.

Ms Adams acknowledged the complex nature of "cold case" investigations, but urged victims of historical child sexual abuse to continue to report incidents.

"Such investigations are often difficult and complex due to the passage of time," Ms Adams said.

"But Tasmania Police actively encourages victims of any crime, and certainly child sexual abuse, to report all such incidents.

"All reports are reviewed by a senior officer to determine the most appropriate course of action in moving forward."

Ms Adams's comments followed a prediction by a West Australian academic that hundreds of people across the country would be reporting cases to police after the start of the national royal commission into child sexual abuse.

In an ABC interview, Professor Caroline Taylor, head of the Social Justice Research Centre at Edith Cowan University, talked about her five-year study that looked at how Victoria Police responded to adults reporting sexual assault.

Aside from predicting a rise in the reporting of historical abuse cases, Professor Taylor criticised Victoria Police for its attitude towards assaults that happened years ago.

Professor Taylor said there were officers worried about a lack of evidence, and others who believed that some were better off putting their abuse behind them.

The royal commission into child sexual abuse started a new phase this week with victims from institutions relating their experiences in face-to-face private sessions.The royal commission will travel across Australia conducting private sessions in capital cities and regional locations.