When the Kerikeri fire brigade arrived, the car was burning fiercely.
Mr Roberts said the driver had a medical condition and may have blacked out. The infant was uninjured, while the child was taken to Bay of Islands Hospital for a check-up. The woman suffered a broken wrist and head injuries, while the driver was merely dazed.
Police inquiries were continuing.
"They were extremely lucky. If they had gone through the gap 200mm the other way they would have collected a thick branch and gone straight down into the creek," Mr Roberts said.
The officer said it was the luckiest escape he had seen in his 12-year policing career.
He praised the Kapiro woman, who had kept her cool and pulled the family from the smouldering wreckage.
"She did very well. That's most people's worst nightmare."
At the very least she would be getting a letter of commendation from the police, he said. After her rescue the woman carried on with her walk, saying she was heading home for a glass of water and a chance to calm down.