One motorcyclist died on Friday and another is in a critical condition after they collided with oncoming cars near Puhoi.
Police believe the men were patched Black Power members travelling in convoy to a Northland tangi.
They are calling for anyone who saw a group of gang members on motorbikes riding erratically on State Highway 1 before 2pm on Friday.
The crash occurred when the two motorcycles - which were travelling on the wrong side of the road - collided with two oncoming cars near Schollum Access Rd.
Serious Crash Unit investigator senior constable Karl Bevin said one rider, a 54-year-old man from Stratford, died that afternoon from injuries he received in the crash.
Another rider, a 50-year-old from South Auckland, remains in a critical condition at Auckland City Hospital.
"We'd like to hear from anyone who witnessed the riders' driving behaviour before the collision or witnessed the crash," Mr Bevin said.
"People with information can contact me on 09 213 4628."
Alternatively information can be provided anonymously to Crimestoppers on 0800 555 111.