Mr Harris said the Fire Service's Manurewa crew and the specialist cutting equipment from Papatoetoe arrived about 8.42am and the boy was taken to hospital about 9am.
St John paramedics were also at the scene and administered pain relief quickly, he said.
A St John spokesman said the boy was transported in a moderate condition transported to Middlemore Hospital.
A school spokeswoman said the boy was "fine" and on his way to hospital for treatment.
"The boy is fine, absolutely fine. He is off to the hospital and the professionals are taking care of him."
She said some students witnessed the accident and were being looked after by staff.