Auckland Police said it is a miracle no-one was killed in a serious crash at an off-ramp on Auckland's south western motorway (State Highway 20).

Police believe alcohol was a factor in the crash which saw a car plough into two others by the Massey Road East off ramp.

One of the cars contained five children between the ages of 2 and 10, who received moderate injuries.

The other vehicle had three children aged 2, 8 and 10 in it - the 10 and 8 year old girls are in Middlemore Hospital with extensive injuries.