The Prime Minister says the punishment for "one punch deaths" may need to be toughened to give a greater deterrent.
There is a push for tougher laws on "king hits" or "coward punches" where the victims fall to the ground and are injured or die but the perpetrator gets a lights sentence.
Mr Key said recent incidents in New Zealand were "definitely worrying".
Asked if there needed to be a greater deterrent, the Mr Key said: "It is worth considering. The Justice Minister would have to look into that".
On Monday, police released CCTV video near Auckland's Fort St of two such incidences which occurred on July 2 just minutes and metres apart.
One victim was knocked unconscious and suffered a fractured nose, stitches to the head, bruises to his elbow and tailbone and cuts on his lips.
The second victim suffered a concussion and displaced jaw, and the second victim suffered a concussion and a wound to his face.
In New South Wales, one-punch assaults causing death if drugs and alcohol are involved have minimum of eight years and a maximum 25 year sentence applies.Newshub.