Two people are dead after a crash on State Highway 1 south of Waiouru shortly after 10pm on Monday night.

Police are continuing their investigations into the fatal crash, which appears to have involved a single vehicle that went over a bank and caught fire.

A Palmerston North man who witnessed the crash told the Stuff website he stopped to give assistance but said the vehicle was well ablaze by the time he managed to stop.

"There was nothing I could do ... right from the start, the flames were too hot."

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Dieter Stalmann said truck drivers with fire extinguishers also tried to help but they were not able to get close enough.

Firefighters from Waiouru and Taihape attended the crash but were unable rescue the occupants of the car.

St John paramedics found two people dead when they arrived at the crash scene at 10.35pm.

Police said last night they had not been able to establish where the occupants of the car were from.