A girl was left hanging upside down a metre off the ground after she slipped while climbing and became impaled on a school fence in Sydney's northwest.
Emergency services were called to a high school in Lawrence Street, Pennant Hills, early this morning when the 16-year-old Wahroonga girl's left leg was pierced by a fence.
Police say she slipped backwards while scaling the 2.2-metre fence.
Fire and Rescue NSW, paramedics and police worked for about 90 minutes to free the girl before she was taken to Westmead Hospital.
Police are hoping to speak to three people she was with, a 16-year-old Pennant Hills girl, a 19-year-old Westleigh man and a 21-year-old man from Pennant Hills.
An investigation is looking into why the group was on school grounds during a weekend night.