A Mongrel Mob member is dead - and two others are unaccounted for - after the car they were travelling in plunged 150m off a bank into Hawkes Bay's Mohaka River today.

The crash happened near the Mohaka Viaduct at 2.40pm, while the trio and another man - who suffered moderate injuries - were travelling to the gang's 50th anniversary party.

Police said all four men were members of the Mongrel Mob.

The police dive squad are heading to Wairoa tonight to begin the search for the two men believed to be trapped in the car.

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A fourth man was taken to Wairoa Hospital with moderate injuries.

The Lowe Rescue Helicopter was dispatched to airlift the man from the riverbank up to the road so he could receive medical attention.

The Fire Service's rope rescue team was also called in to help emergency services reach the vehicle.

Police know the identity of all those in the car but their names have not yet been released.

In another crash in the region, a male motorcyclist was killed around 3.30pm today when his bike collided with a car at Te Haroto on SH5, halfway between Napier and Taupo.

The man's identity is not known at the moment and investigations are continuing into the crash.

The police serious crash unit is investigating both crashes.