UPDATE: A bushfire Emergency Warning alert has been downgraded for residents of Leda, Calista and Medina.
The Department of Fire and Emergency Services said there was a threat to lives and homes from a fire that has burnt through 35ha.
The alert level, which was downgraded to a Watch and Act just after 5.30pm, affects people west of Medina Avenue in Medina, west of Calista Avenue in Calista and the northern part of Leda.
It is not known what caused the fire - which started between Gentle and Wellard roads and at one point was heading towards Kwinana Golf Club - but it is not being treated as suspicious.
The wind shifted in a north-westerly direction and the fire, which is contained but not controlled, is burning towards Mandurah Road.
Burning embers are likely to be blown around homes.
"Spot fires are starting up to 50m ahead of the fire," DFES said.
"If you live in the eastern part of Calista or Leda leave in a northerly direction.
"Do not travel along Wellard Road between Gilmore Avenue and Mandurah Road."
DFES said that if the way is clear, people should leave now for a safer place.
Road closures include Wellard Road, Gentle Road and Stanyford Way.
"Do not wait and see, leaving at the last minute is deadly," DFES said.
"There is an ember attack ahead of the fire, so close all doors and windows and turn off evaporative air-conditioners, but keep water running through the system, if possible."
People who plan to stay and actively defend their home should not rely on mains water pressure because it may be affected.
"If you have access to a water tank and plan to defend your home, start patrolling with your hose and put out spot fires," DFES said.
"If you cannot leave, you need to get ready to shelter in your home and actively defend it.
"If you are not at home, it is too dangerous now to return."
DFES said residents' safest option would be to visit family or friends who live away from the area.
The Department for Child Protection and Family Support has set up a temporary evacuation centre at the Kwinana Town Council building on the corner of Sulphur Road and Gilmore Avenue in Kwinana.
Eighty-five career and volunteer Fire and Rescue Service and Bush Fire Service firefighters from 20 stations and brigades have been tackling the blaze, which was reported at 12.34pm.
DFES State Emergency Service and the City of Kwinana also are at the scene.
Aerial support was sent to protect crews and homes.
A bushfire Watch and Act remains for people in Kwinana Beach, east of Rockingham Road and Patterson Road to the railway line in the City of Kwinana.
Firefighters are also tackling a separate bushfire in the area, with a Watch and Act alert downgraded to an Advice alert tonight for Kwinana Beach and Naval Base.
The warning has been issued for people in an area bounded by Thomas Road, Abercombie Road, Hope Valley Road and Rockingham Road in Kwinana Beach and Naval Base.
There is no longer a threat to lives or homes but there is a lot of smoke in the area, DFES said.
Although there is no immediate danger, people need to be aware and keep up to date in case the situation changes.
"The fire started in bushland north of Thomas Road near Ratcliffe Road," DFES said.
The small controllable bushfire, which was reported at 4.21pm, is moving slowly in a north-west direction.
Ratcliffe Road has been closed as 30 career and volunteer Fire and Rescue Service and Bush Fire Service firefighters from eight stations and brigades tackle the flames.
Firefighters are strengthening containment lines and aerial support has been sent to help ground crews.
The cause of this fire is suspicious/deliberately lit, DFES said.
A bushfire Advice has been issued for residents in Orelia, Kwinana Town Centre and Parmelia.
"Although there is no immediate danger for people in these areas you need to be aware and keep up to date," DFES said.
People are asked to report any suspicious behaviour to Crime Stoppers on 1800 333 000.