A young, homeless couple and their dog have been found dead in their car, apparently killed by a gas heater they were using to keep warm.

Police say the 27-year-old man and 24-year-old woman, both from Ballarat and believed to have been living in the car, were using a butane gas heater to keep the chill away when they died.

Officers found the bodies of the couple and their dog when they checked on the car parked at Smarts Hill Road, near Cardigan, about 9.30pm on Friday.

It is believed the heater may have contributed to their deaths, which the police are treating as accidental.

Nearby residents are still reeling from the tragedy.