"We stand here and condemn, absolutely the attack that occurred today by an extremist, right-wing, violent terrorist," Morrison told a press conference.
He confirmed media reports that the gunman who gunned down several worshipers in the main mosque in the southern New Zealand city of Christchurch was an Australian-born citizen.
He said Australian security authorities were investigating any links between the country and the attack, but declined to provide further details about the Australian gunman.
An emotional Morrison offered his sympathies to Kiwis. "We are not just allies, we are not just partners, we are family," he said.
New Zealand police said they had detained three men and one woman after attacks on two Christchurch mosques, but they have not provided their identities.
"It is such a sad and devastating reminder of the evil that can be ever present about us," Morrison said of the attacks.