Four people, including a five-year-old boy, have been taken to hospital after their car rolled near Palmerston North.
The ambulance service says it was called to the crash on Longburn Rongotea Road about 2.30am on Saturday.
It says two women aged 18 and 23 were taken to hospital in serious condition with head, neck and chest injuries.
A 35-year-old man and a five-year-old boy were also taken to hospital with minor cuts and facial injuries.
The ambulance service says no other vehicles were involved in the crash, which appeared to have happened on a straight stretch of road.