Police are investigating after a "suspicious item" was found at Orelia Oval before a junior football game.
Officers attended the oval around 10am on Sunday after a parent from the Kwinana Knights Junior Football Club found debris on the field.
Nearby residents reported hearing a loud bang earlier in the morning.
Police seized the item for further examination.
The investigation is ongoing and anyone with information should contact Crime Stoppers on 1800 333 000.
Baldivis Police on the lookout for reckless dirt bike riders
Baldivis Police are on the lookout for reckless dirt bike riders.
WATCH: Youths captured on CCTV stealing car in Golden Bay
A group of youths have been captured on CCTV stealing a car in Golden Bay.
Fire crews battle early morning blaze in Warnbro
Firefighters have extinguished a bushfire in Warnbro.
Driver charged over alleged hit-and-run on Mandurah Terrace
A 20-year-old man has been charged over an alleged hit-and-run in Mandurah.
More paramedics, ambulances to be stationed in Dawesville, Australind
More paramedics and ambulances will be stationed in Dawesville and Australind.
Strict demersal fishing bans to come into force off WA coast to save species from extinction
Commercial fishing for demersal fish will be permanently banned off a section of WA's coast along with a raft of other changes to save the under-threat species.
Police call for witnesses to fatal Waroona crash
Police are calling for witnesses to a crash in Waroona that claimed the life of a 55-year-old woman.
WATCH: Confronting footage shows moment car ploughs into teen on Mandurah Terrace
WARNING: This story contains confronting footage.
Teen injured in suspected hit-and-run in Mandurah
An 18-year-old man has suffered a head injury after being hit by a car in Mandurah.