By Allanah Sciberras

Mystery surrounds the discovery of a woman’s body found inside a car that had been parked outside a major police station for days.

Police found the body of a 48-year-old woman under a large blanket in the back seat of a Toyota Yaris parked outside Lake Illawarra Police Station about 4.30pm on Friday.

Assistant Commissioner Joe Cassar told AAP the woman’s body was discovered in an advanced state of decomposition after the region endured several days of severe heatwave conditions.

“Unfortunately, she’s been in the vehicle for so long, it was exceptionally hot within the car,” he said.

“It’s very, very sad.”

Police believe the woman had arrived at the station on Tuesday evening and spoke with officers, although it remains unclear what she discussed with them.

“After spending some time in the station area, the lady exited the foyer and entered the rear seat of the vehicle,” Mr Cassar said.

The woman is believed to have been living inside her car, which was locked when she was found.

Mr Cassar said officers made the grim discovery after noticing the car had not been moved for several days.

The windows had a very dark tint, which was dirty, making it difficult to see inside the car, he said.

“It wasn’t obvious there was a body in there until (an officer) had to break the window … That’s when they were able to discover that in the back seat there was a body,” Mr Cassar said.

“If you looked through the front of the car, you wouldn’t have noticed it.”

Police will spend the coming days reviewing CCTV as part of their investigation into the circumstances surrounding the incident.

A critical incident has also been declared, which is made in cases of police-involved deaths or serious injuries, triggering oversight measures including the involvement of detectives from a different command.

The probe will also be subject to an independent review by the Professional Standards Command and oversight by NSW police watchdog the Law Enforcement Conduct Commission.

Police will prepare a report for the coroner.