Police are investigating an overnight incident which left machinery being used in the demolition of the old Mandurah bridge gutted.
About 1:30am on Wednesday police and fire fighters were called to reports of an excavator on fire.
The excavator was being used in the demolition of the old Mandurah Bridge on Pinjarra Road in Mandurah.
Damage to the excavator is estimated at $100,000.
The fire is being treated as suspicious and investigators would like to speak to anyone who was in the vicinity of the old Mandurah Bridge between 1am and 2am who may have seen any suspicious vehicles or persons in the area.
Anyone with any information is asked to call Crime Stoppers on 1800 333 000 or report the information online at www.crimestopperswa.com.au.
Rewards of up to $50,000 are available for information that leads to the identification and conviction of an arsonist