The worst of the blazes are north of the coastal town of Esperance, 720km south-east of Perth.
Strong winds with gusts up to 90km/h (56mph) have hampered efforts to bring the fires under control.
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""They are the first serious bushfires of the Australian summer.
Authorities said they did not believe the fires were deliberately lit.
"During last night, four people were located deceased in the fire area of Grass Patch, Salmon Gums and surrounding areas in the Shire of Esperance," police said via Facebook.
