The person, found this morning on East Street in Lidcombe near Rookwood Cemetery, had been dead for about two weeks, police said.

"Police were responding to a complaint about a car being abandoned," a police media spokeswoman said.

"They showed up, had a look, and there was a body in there."

Homicide squad detectives and local officers established a crime scene around a green Honda Accord sedan parked at the side of the road.

Two tents were erected as forensic police examined the car and surrounding scene.

"The car has been abandoned there for the last two to three weeks," said neighbour Justin Salar, 22.

"We're all pretty shocked at the moment."

Police said the death was being treated as suspicious.

A witness said he could smell the body when standing downwind from the car.

Neighbours said it was not uncommon for students from nearby TAFE and university campuses to dump unwanted cars in the area.

Two bus routes have been diverted.

Investigators are appealing for anyone who may have any information or witnessed any suspicious behaviour near the car to contact Crime Stoppers.

with Lisa Davies