Victorian Premier Daniel Andrews and health experts are in talks to lift stage four restrictions when virus cases fall to 25 or less a day, with mystery cases, the virus reproduction rate, testing and contact tracing also key to the decision.

Melbourne University epidemiologist Professor James McCaw, who is leading virus modelling for the Commonwealth, told The Australian Financial Review the models predict those daily case numbers are three to eight weeks away, with the state's September 13 deadline most likely a best-case scenario.