Perth woke to a smoky morning on Saturday, with a trough along the west coast bringing low cloud and trapping smoke from fires in Western Australia's south.
The smoke is the result of prescribed burns carried out in the South West — as far away as Walpole — by the Parks and Wildlife Service, private landowners and local government.
A smoke alert has been issued for the Perth CBD and surrounding suburbs.
"Smoke is beginning to clear as the low cloud and temperature inversion lifts and westerly winds strengthen," the alert said.
"Smoke is expected to clear by mid-afternoon today."
Authorities said people with conditions exacerbated by smoke should take precautions in line with their medical advice for these circumstances.
"When we do wake up to find a whole heap of smoke out there we do ask people with asthma to stay calm, just close your doors and windows, put your air-cons on re-circulate, follow your normal asthma action plan," Shelley Harwood from Asthma WA said.
"They might want to limit their outdoor activities and the biggest thing is just monitor those symptoms.
"If [the symptoms] become more severe, or their reliever medication doesn't seem to be working, then they should be seeking medical attention or calling triple zero."
The Parks and Wildlife Service recommended people shut doors and turn off air-conditioners if the smoke was particularly thick.ABC