That patient has since been transferred to Christchurch Hospital via air.
A fourth person, an 18-year-old male, was transported via ambulance to Whanganui Hospital in a serious condition.
The DHB confirmed on Friday morning that the 18-year-old's condition had deteriorated, and he was in a critical condition.
As of Friday afternoon, the 18-year-old was in a stable condition, awaiting surgery.
Waka Kotahi NZ Transport Agency says the crash happened near the intersection with Pauri Rd.
State Highway 3 was closed from the Pūtiki roundabout shortly after the crash, with a detour in place via Fordell.
The road has since reopened after a scene examination by the Serious Crash Unit.
An investigation will follow into the circumstances of the crash.