A blaze that threatened homes at Bakers Hill last night was started from four ignition points.
Residents were told to evacuate or prepare to defend their properties as multiple fires were reported about 10.20pm.
The fires started between Berry Brow Road and Redcourte Road, near Great Eastern Highway.
More than 100 firefighters were battling the out-of-control blaze as it moved west towards homes on Redcourte Road.
Residents on Berry Brow Road, Redcourte Road and O'Driscoll Street were advised to leave or start hosing down their properties.
The bushfire was brought under control overnight and the warning level downgraded to a bushfire advice about 2am.
A police spokesman said initial information indicated the fire was suspicious and the arson squad would attend the scene today.
In recent weeks Northam, Yanchep and Whiteman Park have been hit by a series of suspicious bushfires, with the worst occurring close to the recently built detention centre in Northam on February 6. Detectives identified 11 ignition points in and around that blaze, which eventually swept through five hectares of bush.
In the South West this morning, about 30 firefighters and two water bombers are fighting a fire in Australind that started at Bunbury Golf Club and is burning along Collie River towards Laura Avenue.
The fire was reported about 2.45am and has burned about 10 hectares.
It is a small controllable fire and there is no threat to lives or homes but there is a lot of smoke in the area.
The cause of the blaze is unknown.
Yesterday firefighters battled to save 30 homes and a bird sanctuary threatened by fire in Upper Swan.
The blaze started near the intersection of Great Northern Highway and Apple Street and was reported about 11.30am.
It razed about 150 hectares before it could be brought under control.
Overnight 80 firefighters stayed at the scene and a bushfire advice warning remains in place for people south of Warbrook Road, west of Almeria Parade, north of Millhouse Road and The Promenade and east of Charlottes Vista and Halden Road in Bullsbrook, Ellenbrook, Upper Swan, Belhus, Aveley and The Vines.