The Expressen newspaper reports that the truck hit the school bus from behind, causing it to skid off the road on route 27 near Tranemo, just south of Borås.
Emergency services were called to the scene at 5.45pm, with no initial reports of serious injuries.
“Many of the teenagers are reportedly in shock but we have no information about anyone being stuck in the bus,” Västra Götaland county police spokesman Björ Blixer told the TT news agency.
On the scene, onlookers reported that several passengers were bloodied by the collision.
“There was a fair number of people covered in blood who seemed to be in shock, but no one seemed badly hurt,” one onlooker told the Aftonbladet newspaper.
Police told the paper that two teenagers with serious injuries to the chest and abdomen had been taken to hospital, while there were conflicting reports on how many of the teens had been taken to hospital in total.