Local firefighters were kept busy overnight after five fires were lit in the Kwinana area.
The first started around 8.30pm on Christmas Avenue in Orelia, followed by three on Gilmore Avenue, Medina Avenue and Seabrook Way in Medina and one along Sulphur Road in Kwinana.
The last fire was reported around 10pm.
A Department of Fire and Emergency Services spokesperson said they believe all the fires were deliberately lit.
Anyone who saw any suspicious activity at the time and locations of the fires is urged to contact Crime Stoppers on 1800 333 000.