A three-year-old child and his parents have died in a catastrophic collision with a truck at a rural intersection in Victoria’s south-west.

Police said the family’s vehicle drove directly into the path of a B-double truck after failing to give way at a stop sign about 9.30am Tuesday.

A young boy and two adults have been killed in a crash with a truck in Stoneleigh.

A young boy and two adults have been killed in a crash with a truck in Stoneleigh. Credit: Nine News

Speaking at the scene, major collision investigation unit Detective Inspector Craig McEvoy said the car was T-boned by the truck, causing it to roll before eventually coming to rest on its side.

He confirmed a boy, 3, his 31-year-old mother and 41-year-old father, who had been driving, were killed in the crash.

“It’s a terrible scene … there are catastrophic injuries, and significant damage to the car which made extrication very difficult”.

“What we can establish is that there were three generations of family in a vehicle that was travelling in a westerly direction towards the intersection where a B-double truck was travelling in a southerly direction,” he said.

All passengers are understood to be from Geelong, with the truck driver local to the area.

A fourth woman, the boy’s grandmother, who was seated in the back seat of the vehicle was flown to The Alfred hospital with life-threatening injuries.