Police believe the body they found inside a fiery car wreckage in the early hours of Monday morning was actually a passenger in the vehicle.

The crash occurred at around 2.50am, when the gold Ford Falcon was travelling south on Conroy Street, in suburban Katanning. 

The car crashed into a tree on the side of the road, and caught fire.

It is unknown what caused the car to leave the road.

Ermergency services quickly attended the scene and extinguished the wreckage/

WA Police said a deceased person was found inside the car.

"It is believed that this person was a passenger and they are yet to be identified," spokesman Sergeant Mick Slaughter said.

"Investigators are appealing to the driver and any other persons who were in the vehicle at the time of the crash to contact police.

"They also wish to speak to anyone who came out onto the street after the crash and left prior to police attending."

Anyone with information has been urged to contact Crime Stoppers on 1800 333 000 or make a report online.