"He was killed, he was killed instantly," she said. "They had just called for an ambulance and then the ambulance and things arrived but there was nothing anybody could do for him."
St John spokesman Norm Ngatai said paramedics were called to the scene to treat a male patient aged "around 17 years old".
The resident said the teens, who were not in school uniform, told her they were from Massey and had been playing a game called "possum".
In a separate incident, a 14-year-old girl was taken to Starship hospital at 5.50pm after she was hit by a car on Lincoln Rd, Henderson yesterday.
Mr Ngatai said she had injuries to her face, hands, and legs.
A Starship spokesman said she was in a stable condition last night.
Anyone who may have witnessed the Hobsonville accident is asked to contact the Waitakere police on 09-839-0600.