7 News reports that horrified witnesses have described bodies "flying everywhere".
Paramedics are assessing 19 people at the scene located in Melbourne's CBD, with 12 taken to hospital.
A pre-school aged child has been taken to the Royal Children's Hospital in a serious condition.
Another pedestrian has been taken to the Alfred Hospital. The extent of their injuries it not known.
Police are appealing for any witnesses to come forward.
This article originally appeared on who.com.au