Mr Hendl described the scene as "chaotic".
"[The father] made efforts to get into the car - smashing windows."
A passing doctor immediately started helping the critically injured baby, working on the child for an hour before travelling with the youngster to Whakatane Hospital's emergency department, he said.
"He was obviously a great help. He worked intensively on the poor baby and did a fantastic job," Mr Hendl said.
The baby was transferred to Auckland's Starship Hospital but died there on Sunday night.
The doctor, who works at a Gate Pa medical centre, did not want to speak to the media yesterday.
The baby's 4-year-old sister was flown to Auckland Hospital, where a spokesman said she was in a stable condition.
The children's 26-year-old mother, who was sitting in the back seat with the children, was also injured and was also in a stable condition in Auckland Hospital.
Eastern Bay of Plenty ambulance territory manager Richard Waterson said the grandmother, who was trapped in the car and had to be freed by firefighters, suffered leg injuries.
A Whakatane Hospital spokesman said she was in a stable condition.
Mr Hendl said the crash happened 100m from the scene of another fatal crash last month and the area was a known black spot. In January a man in his 20s died when his car left the road and hit a tree.
Mr Hendl appealed to other drivers to take care in the area. "Please make sure you're refreshed and pay attention and drive safely."
The serious crash unit is investigating. The truck driver was not seriously injured and was discharged from Whakatane Hospital, he said.
APNZ
