One motocross rider has died after colliding head-on at speed with another rider on a dark shingle road, after they had left a party in North Canterbury last night.
Neither man was wearing a helmet and the bikes had no lights on them, police said.
The crash happened in a remote rural area on Cascade Road, Balmoral, near Culverden about 9.45pm.
The man who died was 21-year-old Craig Gordon Pickering, a dairy farmer from Balmoral, police said.
Both motorcyclists were flown to Christchurch Hospital by the Westpac Rescue Helicopter, but Mr Pickering died on the way.
The other rider, a 20-year old man, suffered serious injuries and remained in intensive care, police said.
His injuries were not thought to be life-threatening.
Constable Phil Woods of Culverden police said initial enquiries indicated the two men had been at a party on a nearby property when they decided to go for a ride on motocross bikes.
The two bikes appeared to have collided head-on at speed, and continued on for about 50 metres in each direction before coming to rest, he said.
Mr Woods says enquiries into the crash were continuing and alcohol had not been ruled out as a contributing factor.