Premier Colin Barnett has declared the Northcliffe bushfire a natural disaster as smoke continues to blanket the south of the State and the city, prompting a health warning.
An emergency warning has been downgraded to a watch and act alert for the Northcliffe fire.
The alert level was downgraded following more favourable weather conditions that moderated the fire’s behaviour, the Department of Fire and Emergency Services said in a statement on Friday night.
“There is still a possible threat to lives and homes as the fire is actively burning and conditions could change,” it said.
“The fire is currently stationary due to favourable weather conditions and firefighters are working to strengthen containment lines.”
A bushfire emergency warning remains in place for the southern part of Lower Hotham in the Shires of Boddington, Collie and Williams h where a blaze threatens lives and homes.
About 160 reinforcements from NSW, the Northern Territory and the ACT are due to arrive to join their WA counterparts on Saturday.
They will include incident management specialists, aviation specialists and ambulance officers.
The wind is forecast to change directions several times over the weekend and temperatures in the southwest may hit 40C.
Virtually all of the State's firefighters were committed to the Northcliffe fire and another major blaze at Lower Hotham, in the Shire of Boddington, and there was no likelihood of additional resources.
The Department of Parks and Wildlife has issued a smoke alert for Perth and the South West and Great Southern regions.
The smoke comes from both the Northcliffe and Lower Hotham bushfires and has spread as far north as Geraldton.
The Department of Health is warning people to avoid exposure to the haze, particularly the elderly, the very young and to people with respiratory or heart conditions.
People should take precautions including switching off air conditioners, shutting doors and windows, staying inside and limiting or foregoing outdoor exercise.
An emergency also remains in place for the out of control Boddington fire, which has burnt through 50,000 hectares of bush.
The Department of Fire and Emergency Services warns properties in the vicinity of Quindanning-Darkan Road will be affected by the fire, which will worsen on Friday due to unfavourable weather.
The fire was stationary overnight, as cooler weather and drizzle allowed firefighters to focus on containment lines before hotter weather arrives and the wind direction changes.
The maximum temperature on Sunday is forecast to nudge 40C.
A fire in Kwinana last night added to the smoke over the city.
A bushfire advice was issued for people in the southern part of The Spectacles in the City of Kwinana yesterday after a fire started about 3.20pm near the corner of Thomas and McLaughlan roads.
About 100 firefighters and aerial support fought the blaze and had it under control by evening.