The mask mandate has returned for Perth and Peel residents after WA recorded 18 local cases in the past week.
From 6pm on Sunday, masks will be required for all public indoor venues, including the workplace.
They won't need to be worn in the home or apply to people doing vigorous indoor exercise or children under 12.
The move comes after five local cases were reported in WA as of 1pm on Sunday.
Four of those cases are linked to U Natural Spa Therapy in Applecross.
"I implore anyone who has visited this business between the 7th and 13th of January to please come forward and get tested immediately," Premier Mark McGowan said.
"Do not hesitate, do not assume you are fine because you have no symptoms. You must go get tested.
"What we know from the Omicron experience over east is that you can be carrying the virus with you, and have no symptoms. So don’t leave it until it is too late – go get tested now."
A list of exposure sites can be found here.
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