Mr Singer said there was no evidence to suggest another vehicle was involved, however police were in the process of talking to a number of witnesses to the crash.
Eastern District Serious Crash Unit Senior Constable Cory Ubels said the car driven by Dwayne left the road just after 8pm. His body was found by emergency services inside the overturned Honda hatchback in a paddock.
"All we know is the car has driven off the road and down a very steep bank," said Mr Ubels.
The 18-year-old passenger was flown to Hawke's Bay Hospital by the Lowe Corporation Rescue Helicopter from the scene, eight kilometres west of Waipawa.
Mr Singer said the 18-year-old had head injuries and a hospital spokeswoman said he was in a stable condition yesterday.
"He has managed to free himself from the car, or has been flung from the car, we are not sure yet but when we arrived he was well outside the vehicle," said Mr Singer.
Mr Ubels said it was too early to know how the accident occurred.
A blood sample had been taken from the 18-year-old, however he was unable to confirm whether alcohol was a factor in the crash.
There have now been six lives lost on roads in the Wairoa, Hastings, Napier, Central Hawke's Bay and Tararua districts this year.
It compares with 17 at the same stage of last year, which included two multiple-death crashes which killed eight people in Northern Hawke's Bay.