Ballarat Sergeant Brendan Cosgriff said the blaze started in the backyard of a vacant Grevillea Road house at 4.30pm.

“It was a vacant premises and the fire has spread to the house and engulfed a lot of the inside of the house,” he said.

“At this stage it’s suspicious because the house was vacant and we haven’t determined how it started.” Sergeant Cosgriff said the owner of the property had not been living in it for some time, but there was still furniture inside.

Firefighters arrived within a couple of minutes of the triple zero call and brought the blaze under control.

Thick smoke blanketed the neighbourhood, bringing dozens of curious residents out of their houses to observe the commotion.

Wendouree CFA captain Garry Drabsch said the station was on high alert due to the heatwave conditions so firefighters were on the scene quickly.

But when they arrived the fire had already spread through the roof space, he said.

Mr Drabsch described the damage as “total loss”.

Neighbour Sergio Carlos said he was washing his car when he noticed smoke coming from the property next door. “It started as a small fire and just engulfed quickly,” he said,

His partner Shanae Seubert said they knocked on the door to make sure nobody was home, before calling triple zero.

One man who lived nearby said at one point the smoke was so thick he could not see the cars parked in the street.

Police are asking for any witnesses to contact Ballarat Police Station on 5336 6000.