The man died at the scene, police said in a statement.
Videos posted online showed panicked shoppers running out of the LynnMall Shopping Centre and looking for cover as the situation unfolded.
Six people have been injured, according to CNN affiliate Radio New Zealand, citing emergency services. Three are in critical condition, one is in serious condition and the other two are in moderate condition.
Heavily armed police and ambulances remain at the scene.
“The matter is now in the hands of the police and we’ll continue to provide them with our full assistance,” the mall said in a statement on Facebook. “LynnMall is now closed and we will update once we know more.”
This is a developing story.