The judicial inquiry into Victoria’s botched hotel quarantine program is gathering evidence to show whether every case in the current COVID-19 outbreak can be traced back to "completely unacceptable" breaches by private security guards hired by the Andrews Labor government.

The opening day of the inquiry came as Victoria continued to ride the “numbers roller-coaster” with 275 new cases and more than 5 million Melburnians prepared to wear masks from Thursday, as economists expect the state’s outbreak would set back the nation’s economic recovery.