POLICE are investigating an incident in which a man was hit in the head, threatened with a knife and had his bag stolen
Police said the incident occurred in Greenfields on Thursday night and resulted in a 23-year-old man being injured.
It is alleged about 10.45pm, the 23-year-old man was walking along Waldron Boulevard and as he approached Wildair Street he noticed a man on a BMX heading towards him.
The rider of the BMX stopped and struck the victim to the back of the head, causing him to fall to the ground.
The offender then threatened him with a knife before stealing his bag and riding off.
The victim was treated in hospital for a head and shoulder injury received during the robbery.
The offender was last seen riding east along Waldron Boulevard towards Murdoch Drive.
He is described as being 18 to 20 years old, with brown skin and a slim build, about 178cms tall with short dark hair, wearing shorts and a hoodie.
Police would like to speak to anyone who was in the area around the time of the incident who may have seen a person on a BMX bike.
Anyone with any information is urged to call Crime Stoppers on 1800 333 000 or report online at www.crimestopperswa.com.au.