A couple, friends of the victims who did not want to be named, said they watched in horror as the driver lost control, hit the tree and the car snapped in half.
"The car just shattered,'' said the woman, who lives nearby.
"This used to be a gravel road and cars would often go around the corner and slide off into the bank but I have never seen anything like what happened last night ... It looked like an explosion.''
The witnesses said two big pieces of the vehicle were left several metres apart.
The woman rang emergency services within seconds of seeing the crash and her partner ran to the scene from where he had been milking cows to see how he could help.
He checked the driver for a pulse but he was already dead.
The second man, who had been thrown into a ditch along with his car seat, was still breathing.
"His breathing kept slowing and then speeding up again. I just stayed with him until the ambulance arrived ... They were good friends.''
McLaren Falls Rd was blocked for several hours while police analysed the crash site to find out exactly how the accident happened, and traffic was diverted back to Omanawa Rd and State Highway 29.
Acting Senior Sergeant Cameron Anderson said the two men were travelling southbound _ away from the highway _ when the car went off the road.
"[They] came over a slight rise, left the road, crossed the centre line and crashed into a large tree. The impact caused the vehicle to split in two,'' he said.
"The car was in two pieces. There was a front half and a back half, he said.''
Photos of the destroyed car show the impact was just behind the front wheel on the driver's side.
"It was a sealed road ... it was a straight piece of road.''
Mr Anderson said the serious crash unit was investigating but speed had already been identified as a contributing factor.
He said the men did not live on the road and it was unclear where they were going.
The crash was one of three serious incidents on North Island roads overnight.
Two others were killed after the vehicle they were travelling in rolled on State Highway 5 at Rangitaiki, south of Taupo, about 2.20am.
Three other people were transported to hospital with minor injuries.
That followed a single-car crash in nearby Mihi about 11.30pm.
A man suffered serious head injuries and was transported by helicopter to Waikato Hospital in a critical condition.
