A West Australian woman who visited Sydney and returned home has picked up COVID-19, prompting increased restrictions including mask wearing indoors.
WA Health Minister Roger Cook on Sunday said the Perth woman was earlier this month in the Bondi area of Sydney.
It is assumed the woman - who tested negative to COVID-19 when she returned to WA - has the Delta virus variant.
Mr Cook said Perth and Peel region residents would immediately be required to wear masks indoors and on public transport.
Public events will be restricted to 150 people, while Sunday's AFL match between West Coast and Western Bulldogs will go ahead without crowds.
The Chicken and Beer Festival in Perth scheduled for Sunday has been cancelled.
A 30-person limit is in place for private gatherings and Perth and Peel venues must adhere to the "two square metre" rule.
Travel to WA's remote Indigenous communities will be restricted.
Mr Cook didn't rule out lockdown as a future necessity, with the current restrictions to remain in place for at least three days.
"We are watching the situation in NSW and seeing just how quickly and easily the Delta variant is transmitted within the community," Mr Cook told reporters.
"This is a proportionate response.
"These decisions aren't easy but we believe that they're very necessary because we, at this stage, don't know the nature of the threat."
A hard border has already been reimposed in WA for NSW residents, currently in lockdown due to the growing Bondi cluster.
Mr Cook also didn't rule out reimposing a hard border for all other Australian states as COVID-19 outbreaks occur across the country including NSW, Queensland and the Northern Territory.
