The police in Porirua say four motorcyclists involved in a crash with a car are gang members.
The crash happened on State Highway 1 north of Wellington at about 12.30pm on Saturday.
Police say the motorcyclists, from the Highway 61 gang, were riding from Wellington to Paraparaumu.
Constable Grant Nalder says five motorcycles were travelling together in a group from Wellington to Paraparaumu when two of them tried to pass two cars on a bend.
"Two motorcycle riders have attempted to pass two vehicles, they were travelling side by side. One of them has got through safely, the second bike has clipped one of the vehicles and then that has created pile-ups.
"There were four bikes went down in total."
Mr Nalder says the car went into the barrier arm.
Police appeal for witnesses
Six men aged in their 40s to 50s have been taken to the Wellington and Hutt hospitals.
A Dannevirke man, 47, has a suspected head injury and another of those injured has serious back and abdominal injuries.
The police are appealing for witnesses to the crash as well as the first motorcyclist, who succeeded in overtaking the cars and carried on.
The road was closed to northbound traffic for several hours, causing long delays for motorists, but it has since reopened.