The spokesman said one ambulance and a scene manager was sent to the incident, on First View Ave about 4.45pm.
Police said the incident had not been reported to them.
Beachlands Fire Station were called to the job and used specialist cutting equipment to detach part of the stake so the boy could be transported by helicopter.
"It's an unfortunate accident," said chief fire officer Shane Rutherford. "He was very lucky to still be alive, he had somebody watching over him."
Mr Rutherford said the special cutter was like a miniature grinder that made no vibrations.
"We had to keep him 100 per cent still. He was very calm and collected, he is very courageous."
The stake was a metal pole used to attach real estate signs into the grass in front of homes.