POLICE are investigating a serious robbery where a woman was injured and had to fight off three men with a didgeridoo.

Three men broke into a unit in Ormsby Terrace in Mandurah just after 5.10pm on Friday.

They demanded property from the victim, a woman in her 40s, who asked them to leave.

Police said the woman ran to escape but one of the men physically restrained her and struck her in the face during a short struggle.

Another man searched her belongings and pulled off the gold neck chains she was wearing.

The woman managed to break free, picked up a didgeridoo and swung it at the men.

Police said the men were seen fleeing in a white sedan, similar to a Holden Cruze.

Detectives would like to speak to anyone who may have witnessed the incident or may have captured the men leaving the unit in the white sedan on dash-cam.

Anyone with any information is urged to call Crime Stoppers on 1800 333 000 or report online at www.crimestopperswa.com.au.