A woman’s body has been found in bushland, triggering a homicide investigation amid fears she might be a victim of foul play.

A passerby discovered the body, believed to be a middle-aged woman, in Werrington, in Sydney’s west, on Sunday afternoon, NSW police said.

“It appears as though that body has been there for a period of time without discovery,” Detective Superintendent Trent King said.

A crime scene was established, with forensic officers examining the remote area of a bush reserve near sporting fields and homes.

How the woman died and why her body, found with clothing and rubbish, was in the bushland are yet to be determined.

“Until we identify the cause of death, the death is unexplained and certainly in this circumstance we feel it necessary to take it to the highest level until we can disprove that situation,” King said.

The passerby is helping detectives with the investigation.

Anyone with information that could assist police has been urged to contact Crime Stoppers.

-AAP