It was thought the boy slipped off the track and his father fell trying to help.
Wayne Price who lives near the access to the Omanawa Falls underground powerstation said it was the third mission by the rescue helicopter to the falls.
During summer weekends, it was common to see 15 to 20 cars parked at the top of the access, with about three-quarters belonging to young people going down for a swim.
Mr Price said Tauranga City Council, which owned the powerhouse, had put up a warning sign and fence to try to stop people accessing the falls via a track along a ridge and around the top of the falls.
Craig Jones, the St John intensive care paramedic who was in the rescue helicopter, said the thick scrub would have stopped their fall.
It was a complex rescue mission in which the man was first winched out and taken to the top of the gorge to receive medical attention. They then returned and winched up the son, picked up the father and flew to Tauranga Hospital.
Mr Jones was notified about the operation at 3.45pm and the helicopter did not reach the hospital until 6pm.
An ambulance crew, a fire crew and bystanders were there when he was winched down from the helicopter to the injured father and son.
Mr Jones said the dad was worried about his unconscious son. However, by the time the boy was put in the harness to be winched up, he had regained consciousness and was talking to him. "That was fantastic."