Two people on the bus suffered minor and moderate injuries and were taken to Auckland City Hospital but no information was immediately available this morning on their conditions.
Witness described hearing children crying and seeing a toddler in a party dress being pulled from the back of a car.
Mt Eden local Mikey Beban was one of the first at the scene, and called 111.
He was about 30m away from the crash when he heard an "almighty bang".
A white car had been shunted to the side of Mt Eden Rd and he could hear children's crying coming from the back seat. A toddler in a party dress was brought out of the back seat and attended to by emergency services at the scene.
A baby was also brought out. The baby appeared to stop breathing but ambulance staff, who had just arrived, were able to intervene, Beban said.
An off-duty nurse and paramedic were at the scene.
"In that short time the guy passed away. The sad thing is someone is waiting at home for their [children] and maybe their husband."