"It had impaled his thigh on one side and could be seen protruding on the other. It had gone straight through and made quite a serious wound on the entry side."
However, the boy remained calm despite the accident, he said.
"The kid was as brave as they get ... I felt real sorry for him. Most adults would have been screaming their heads off."
Police and firefighters lifted the bike off the boy, who was being supported by his parents and sister.
St John ambulance staff arrived shortly after and gave the boy pain relief before firefighters used a cordless saw to cut the branch down in size.
"Even once we'd cut the branch and moving it, it's really difficult not to cause a bit of discomfort but he was really good, everyone was really impressed."
Papamoa police Constable Shane McCarthy said the victim was a "brave little boy".
He was moved into an ambulance and taken to Tauranga Hospital with a badly broken leg. The remainder of the branch was to be removed once he was admitted.
Senior Sergeant Glenn Saunders said the accident was a reminder that parents needed to be aware of the risks associated with motorbikes.
"Obviously, you have to be aware of the risk involved regardless of how skilled the young boy is."
