All three people who died in the two-car smash in Hamilton about midnight were in the same vehicle, a Holden Trax, and the police want to hear about the movements of the other car involved, in the lead-up to the crash.
Two women and a man died in the collision just after midnight - two of the dead were from the same family.
Two others were taken to hospital with serious injuries.
Detective senior sergeant Ross Patterson said the police are working to piece together what happened in the lead-up to the crash.
They would like to hear from anyone who saw a blue and grey Toyota Prado speeding on the Hamilton Expressway between 11.45pm and just after midnight.
Anyone who saw the actual crash is also being asked to come forward.
Mr Patterson said the roads were dry and the weather was clear when the crash happened.