First reports came in at about 01:00 local time (5pm Sunday NZT) of a shooting outside a bar in the Oregon district of the city.
Casualties have been taken to a number of hospitals, according to local media.
At least 9 people have been killed.
The incident came hours after another mass shooting in El Paso, Texas which left at least 20 people dead.
It is unclear whether the shooter is still at large. Police have appealed for witnesses.