The crash took place on the D’Aguilar Highway near Nanango, north-west of Brisbane, at about 5.45pm.
Police said the three occupants of the car, an 81-year-old woman, an 84-year-old man and a 54-year-old man, were killed in the crash.
The driver of the truck, a 52-year-old man, has been taken to hospital in a stable condition after suffering minor injuries.
Police said the highway would remain closed in both directions today, with diversions in place.
Drivers are urged to avoid the area.
Any witnesses or anybody with dashcam footage or CCTV is urged to contact police.
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