The man died at the scene, police said in a statement.
Videos posted online showed terrified shoppers running out of the LynnMall mall and seeking protection as the situation unfolded.
Four injured people were taken to the hospital, according to Citizen Free Press affiliate Radio New Zealand. Two are in critical condition.
Heavily armed police officers and ambulances remain at the scene.
“The matter is now in the hands of the police and we will continue to provide our full assistance to them,” the mall said in a statement on Facebook. “LynnMall is now closed and we will update once we know more.”
Prime Minister Jacinda Ardern is being briefed on the situation, a spokeswoman said.
News in development.
Reuters contributed reporting.