Three people have been killed in a crash between a truck and a car near the town of Birdwood in the Adelaide Hills.

Police said emergency services were called to the scene, at the junction of Martin Hill Road and Lucky Hit Road, at about 1:40pm yesterday.

Three passengers — a 64-year-old man, a 27-year-old woman and a 22-year-old woman — in the Toyota sedan died at the scene.

The sedan driver, a 73-year-old man, had life-threatening injuries and a fourth passenger, a 56-year-old man, was seriously injured.

Both had to be cut from the wreckage before being flown to the Royal Adelaide Hospital.

The 50-year-old truck driver from the state’s Mid North, who was not physically hurt, has been helping police with the investigation.

Major Crash  investigators headed to the scene and police closed multiple roads in the area, which have since reopened.

Resident and former CFS captain Michael Bell, from nearby Forreston, said he made his way to the intersection to try to assist.

Forreston local Michael Bell attended the scene to try to offer assistance. (ABC News)

“The scene is fairly confronting,” he said.

“The truck is sort of crossed up at the intersection [and] the black sedan is off to the left-hand side, off the road, and emergency services are everywhere.”

Mr Bell said he did not know the victims, but expressed his condolences.

“That was my first concern. Obviously, being a local, you’re concerned that it is a local,” he said.

“But my heart goes out to that family anyway, whoever they are.

“There’s a lot of people going to be hurt tonight.”

Mr Bell said the intersection had a “notorious history of bad accidents”, and both he and another resident, Jim Rathjen, said a child had been killed there in recent times.

“It’s bad enough having a crash, but when they’re fatal it’s shocking,” Mr Rathjen said.

“Three lives lost. It’s not only those three — it’s their families [affected] as well.”

Police responded to a road crash in which a truck hit a car yesterday. (ABC News)

He urged people to drive to the conditions, especially heading into the Easter long weekend.

The deaths bring the total lives lost on South Australian roads this year to 26.

Two-car crash in Fleurieu Peninsula

Meanwhile, a man was seriously injured when a Holden station wagon and a Toyota four-wheel drive collided in the Hindmarsh Valley south of Adelaide.

Police were called to the scene at the intersection of Victor Harbor Road and Hindmarsh Tiers Road about 2:15pm yesterday.

The driver of the station wagon, a 65-year-old Normanville man, was flown to hospital with serious injuries.

“The passenger of the Holden was treated at the scene by SA Ambulance for minor injuries and was conveyed to hospital,” police said.

The driver of the other vehicle, a 36-year-old Port Noarlunga man, was treated at the scene for minor injuries.

Police are asking for any witnesses of either road crash who are yet to speak with officers to contact Crime Stoppers.