Authorities say a bushfire that posed a possible threat to lives and homes in East Rockingham and Kwinana was deliberately lit.
The fire started near the intersection of Patterson Road and Charles Street around 3.18pm on Monday.
It reached a watch and act alert with nearby residents urged to leave their homes or get ready to actively defend them.
Firefighters managed to bring the blaze under control within a couple of hours.
It had burnt through 2.5 hectares of bushland.
Anyone who saw any suspicious activity at the time of the fire should contact Crime Stoppers on 1800 333 000.

A bushfire advice remains for the area. PIC: DFES
Green thumbs, families invited to Pinjarra Garden Day
NBL1 West: Devondrick Walker announced as new coach of Mandurah Magic men
Two drivers killed in horror Peel region crash
Arson Squad detectives continue investigation into Port Kennedy house fire
Peel Thunder premiership coach Adam Read to depart club for GWS
Man wanted for questioning over Wellard scooter theft
New murals to transform Coodanup, Madora Bay public spaces during Mandurah Arts Festival
Teen driver allegedly three times over legal alcohol limit in Rockingham
New councillors elected in Rockingham, Mandurah