Armed police are guarding the entrance to an apartment complex on Gore Street in central Auckland.
An RNZ reporter saw about five police cars at the scene and a number of ambulances on Monday morning.
Two police officers were guarding the door of Auckland Harbour Suites, questioning witnesses or residents.
In a statement, police said at least one person was injured.
"At this stage, we do not believe there is a wider risk to the public in relation to this incident."
Inquiries into the exact circumstances surrounding the incident were ongoing.
Police cars had arrived about 7.15am and officers armed with assault rifles made their way to the apartment building.
About 12 police officers with firearms were seen.
Two further ambulances arrived around 7.50am but there appeared to be no panic or rush.
One resident who had lived at the complex for three years said he was on his way to work when police asked to take down some information from him.
He heard nothing before police arrived and said police activity at the apartment building was unusual.
