Police were alerted to a disturbance involving two groups in Alexandra St, in the central city, about 12.10am today.
RNZ understands the victims were stabbed.
Area manager investigations Detective Sergeant Reece Durston said four people were injured at the scene, and a 20-year-old man died in hospital a short time later.
The other three suffered injuries ranging from moderate to serious.
"Some of those involved, including the offender, left the scene immediately after the incident."
The investigation team was trying to find them and also any weapons used.
"This is a senseless act of violence," Durston said.
"The investigation team is working hard to understand how and why this happened, and we are wrapping support around the family of the deceased and the other victims."
There would continue to be a visible police presence in the city as inquiries continue, as well as reassurance patrols in the community.
Sources have told RNZ the alleged stabbing may have been linked to a club event in the central city.
The person, who did not want to be named, said the central city was heaving last night following the All Blacks third test against France at FMG Stadium.
Bar workers were unable to access their cars parked on the street and were told by police to either walk home or Uber, sources said.
Alexandra St has been cordoned between Collingwood St and Hood St, and was expected to remain closed through the day.
"There is a large scene to work through and we ask that the public avoid the area and thank them for their understanding," Durston said.
Simon Bowman, of Beast Style Fitness, said today the gym remained shut as its premises is inside the cordon.
Dozens of guests staying at a hostel in Alexandra St have been asked to stay put.
Sabina, a manager at the Hamilton City Inn, said about 50 people were at the hostel.
The cordon includes a car park, and anyone with a vehicle there is asked to make a report online, or by calling 105.
Please use the reference number 250720/3051.
