The true number of people infected with COVID-19 in Australia is likely to be much higher than the official government tally, experts say, with one estimate putting the figure as high as 30,000.

There have been 6623 confirmed COVID-19 cases in Australia so far, but independent epidemiologists said that number is likely to be a significant underestimate.

Any underestimate of the true spread of the virus might encourage false confidence in the timing of any government decision to relax Australia's lockdown, some experts warned.

A model developed by the Actuaries Institute suggested the true number could be five times higher than the official number of diagnoses.