Two homeless people believed to have been using a butane heater to keep warm in their car have been found dead on the outskirts of Ballarat in central Victoria.

Police found the bodies of the 27-year-old man and 24-year-old woman inside the car, which was parked on Smarts Hill Road in Cardigan.

It is believed the pair had been living in the car and were using a butane heater to keep warm.

Their dog was also found dead in the vehicle.

Police made the discovery while checking on the car around 9:30pm on Friday and were not treating the deaths as suspicious.

The coroner will investigate whether fumes from the heater contributed to the deaths.

Dr Bruce Redmond from the Salvation Army said it was a sad reminder of the difficulties facing homeless people in winter.

"I think a lot of us have been complaining about the cold and really been feeling it this year," he said.

"But there are many people who are doing it tough who don't have a roof over their heads and having to live in cars or live on people's floors or on their couches.

"That's one of the real faces of homelessness that we're seeing more and more of."

Dr Redmond said keeping people warm during winter was one of the Salvation Army's biggest challenge in Victoria.

"[We] are certainly stretched to the edges in terms of helping people with blankets and with assistance to heat their houses and that type of thing," he said.

"It's a pretty tough time of the year and I think it reminds us of just how tough people will do it."