Three people were injured - two seriously and one moderately - after the two-car crash on Ti Rakau Dr in Pakuranga about 9.25am.
One of the cars, a Honda Civic, was left severed in two and the key Auckland road was closed as the Serious Crash Unit began investigating.
A witness said he believed the child involved was under 10 and had received significant, life-threatening injuries.
The child is believed to have been a passenger in a BMW and had to be cut from the vehicle.
The driver of the second vehicle, the Honda Civic, is believed to have been thrown from the vehicle.
The witness said he understood one of the vehicles - believed to be the Honda Civic - was "pink-stickered" some days before the crash.
A pink sticker, which directs that the vehicle is not to be driven on a road, may be issued to the driver or owner of a vehicle by an enforcement officer who believes on reasonable grounds that a vehicle is not in a safe condition to be driven on a road.
A pink sticker remains in force until the vehicle has been inspected and a new WoF or CoF has been issued.
"It appears one vehicle has crossed the lanes and turned into a side road. It was hit side on, on the passenger side, and ripped in half," he said.
The witness believed speed was a significant factor.
Police would not confirm whether either of the vehicles involved was pink stickered.
This morning's crash came after another serious crash in east Auckland last night, in which a person was killed.
The crash occurred on Te Irirangi Dr in East Tamaki around 11pm.
One person was trapped and died a short time later.
The Serious Crash Unit is also investigating this incident.
