The man died at the scene, police said in a statement.
Videos posted online showed panicked shoppers staying out of the LynnMall mall and seeking coverage as the situation unfolded.
Six people have been injured, according to CNN affiliate Radio New Zealand, which cites emergency services. Three are in critical condition, one in serious condition and the other two in moderate state.
Police and heavily armed ambulances remain at the scene.
“The matter is now in the hands of the police and we will continue to provide them with all our assistance,” the mall said in a statement on Facebook. “LynnMall is already closed and we will update it once we know more.”
Prime Minister Jacinda Ardern is being briefed on the situation, a spokeswoman said.
This is a developing story.