Sydney bridge death suspicious: police

The death of a man whose body was found under a bridge in a western Sydney park is being treated as suspicious and may be another targeted shooting murder.

"Severe head injures" were found on the body, which was discovered under the Duck River Bridge at Mona Park, Auburn by a local man during his morning walk on Thursday, police said.

The dead man is believed to be in his 20s.

No weapons have been found, but Superintendent Phil Rogerson said "there's quite a probability that a weapon has been used and no doubt a firearm."

Witnesses have reported hearing noises, but Supt Rogerson wouldn't confirm if these were gunshots.

"I can't say it's targeted," Sup Rogerson told reporters.

But the "lines of inquiry" police are taking means it is a possibility, he added.

The man hasn't been identified and no one has reported any missing family members.

Police are canvassing the area and forensic specialists will spend the next few days trawling for evidence in and around the popular park.

Divers will also be sent into the Duck River.

The body will be removed on Thursday afternoon and post-mortem results are expected on Friday.