The victims included a 45-year-old man, a 38-year-old woman, a 2-year-old boy and two girls, aged 11 and 13, police confirmed on Tuesday.
The driver of the truck was also taken to hospital where he was treated for shock following the accident.
Falling snow made for poor visibility and slick roads when the driver apparently lost control of the car, causing it to cross into oncoming traffic and into the path of the truck.
“The long-haul truck was carrying a heavy load of wood chips,” Per Larsson of the Lidköping police told the TT news agency.
The accident took place around 8.30pm as the car was traveling north on the two-lane E20 motorway near Skogsbo, just south of Vara in western Sweden.
Snow had been falling in the region and the roadways were slippery and covered in slush when the two vehicles collided head-on.
The truck pushed the car for around 60 metres before tipping over and coming to rest in the ditch.
Rescue workers were forced to cut open the car to reach the passengers, but discovered all had perished.
According to the duty officer with emergency services in Gothenburg, the car was carrying two adults and three children.
Several hours following the accident, police continued their work to identify the victims, theorizing that it may have been an entire family.
“It’s not unlikely,” Larsson told the Aftonbladet newspaper.
He added the police are still looking into the cause of the crash.
“We have no idea what happened or whose fault it may be,” Larsson told TT.