Police said a suspect had been arrested following the shootings, which occurred around 1:00 am (2300 GMT Friday) in three locations, including a gay bar, close together in the center of the Norwegian capital.
Police reported two dead and 14 wounded, and said two weapons had been seized, France 24 reported.
"Now everything indicates that there was only one person who committed this act," police official Tore Barstad told a press briefing.
Police numbers had however been reinforced in the capital to deal with other incidents, he added, without wishing to specify whether it was a terrorist act.
MA/PR