Fire crews are responding to multiple fires lit along the Great Eastern Highway, east of Perth.
Authorities say three were lit at Beechina, one at Mokine, another at Clackline, one in Northam and another at Woorooloo.
Water bombing aircraft have been sent to assist ground crews battling a large scrub fire opposite the Yongah Hill Immigration Detention Centre in Northam.
A watch and act has been issued for the western part of Northam, in an area bounded by Great Eastern Highway, Mitchell Avenue and Verlinden Road.
The Department of Fire and Emergency Services says there is a possible threat to lives and homes as the fire is approaching the area and conditions are changing.
DFES says residents need to leave or get ready to actively defend.
A number of roads have been closed, including the Great Eastern Highway between Clackline and Northam-Toodyay Road.
Crews have been diverted from Boddington, south-east of Perth, where they were fighting an out-of-control blaze which has destroyed a house.
That blaze is now contained.
Firefighters are also battling a fire in scrubland at North Coogee, south of Fremantle.
Several roads are closed and motorists are being asked to avoid the area.