South-west residents will once again need to don a mask at their workplace or secondary school as of 11.59pm Wednesday.
Victoria's acting chief health officer Clare Looker announced the directive at 10.30pm Wednesday.
It comes after 11 new COVID-19 cases were declared in the state on Wednesday, including a Bacchus Marsh Grammar school staff member.
The new mask rules are for people aged 12 and above.
Victorians must wear masks indoors, except at home, unless an exemption applies. The rule applies to both workplaces and secondary schools.
Masks must also be worn outdoors where people cannot maintain a 1.5-metre distance from others who aren't from their household.
The department stated more information would be available via http://coronavirus.vic.gov.au after the new direction came into effect.
Previously, face masks were mandatory indoors unless an exception applied, or if people were: at home; at work in an area that members of the public could not normally access, such as an office space or a factory; a staff member at a school, childcare or early childhood service, and a member of the public wasn't present, apart from at reception where masks were always required; or a student at school.