The Arson Squad is investigating a deliberately lit fire at the Mandurah Forum.
A Department of Fire and Emergency Services spokesperson said the centre's automatic alarm system was triggered around 12.58am on Friday.
The fire is understood to have started at the back of Kmart.
It was brought under control by 2am.
A damage bill has been estimated at $100,000.
The cause has been deemed as suspicious.
Anyone with information is urged to contact Crime Stoppers on 1800 333 000.
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