A teenage boy has been charged after a 12-year-old schoolgirl was slashed 20 times in the face during a vicious assault south of Brisbane.

The girl was allegedly attacked as she was walked through a pedestrian pathway under the Logan Motorway at Kingston about 7.40am on Thursday.

A 17-year-old boy has been charged with acts intended to cause grievous bodily harm after a manhunt that involved about 30 police officers.

Detective Acting Inspector Grant Ralston said the girl had been walking alone to school when she was targeted “for no reason”.

“The male is believed to have had possession of some sort of cutting instrument, like a box cutter, and continually struck the young girl on the right side of the face causing extensive injuries,” he said.

“She fought as best she could and eventually after being struck approximately 20 times to the face, incredibly, she managed to pick herself up and run towards her school at Kingston.”

The girl was bleeding profusely and was taken to hospital where she underwent surgery.

She told police the attack had only taken 10 to 15 seconds.

“The young girl is very brave,” Ralston said.