Two vehicles who appeared to be looking at the crash at the roundabout also crashed, Donnison said.
A 37-year-old man was later arrested and the vehicle found in Flaxmere.
The man is yet to be charged.
"Police would like to thank the members of the public who reported a suspicious vehicle in their area which led to police finding the offending vehicle and driver at an address," Donnison said.
Takapau resident Dave Smith, who was involved in the secondary crash, said he was travelling south along the expressway when he had to stop because traffic had piled up.
"All the traffic had stopped because there were sirens."
He had just started moving again over the roundabout when he had a minor crash with another car.
A male passenger and a young boy in his car, as well as those in the other car, were uninjured.
A Hawke's Bay Hospital spokeswoman said the three women admitted to the hospital - two aged in their late 30s and one in her late 20s - had been discharged.
The baby was still in hospital in a stable condition.
The police serious crash unit will be investigating.
