The incident is believed to have occurred in the St. Hanshaugen neighbourhood of the Norwegian capital during Wednesday night, reports broadcaster NRK.
“He is a man in his twenties. He is not familiar with Oslo and was therefore unable to say exactly where he was when he was shot,” operation leader Rune Hekkelstrand of Oslo Police told the broadcaster.
“He was in contact with another person, who at some point produced a weapon and shot the victim several times.”
A number of witnesses saw the man after he was shot but were unable to confirm the exact scene, according to newspaper Dagbladet.
The man, who according to police is a Swedish citizen, conveyed himself to the city's Ullevål Hospital, where he arrived just before midnight with a number of shooting wounds.
Police wrote on Twitter that the man was seriously injured and that they were “working on collecting information relating to the scene of the incident.”
Vi jobber med å innhente opplysninger om hvor åstedet for hendelsen er. Fornærmede er en mann i 20-årene.— Politiet i Oslo OPS (@oslopolitiops) March 22, 2017
“We believe it is somewhere in St. Hanshaugen, but we do not have a specific place. We have not found any evidence that can tell us where this incident occurred,” Hekkelstrand told NRK.
Police have been given a description of the suspected shooter, but have so far chosen not to make this public. It is also unknown whether the two men involved in the incident were in contact with others at the time, reports NRK.
“We cannot make any comment on motive at this time. We have been given a description of the suspect but do not wish to make too many details public out of consideration for ongoing interviews and investigation,” Hekkelstrand said.
Interviews of the victim will be completed during the course of Thursday, police said.
A second man, said to be known to the victim, spoke to the police and has now been placed under arrest for giving false information.
Hekkelstrand told Dagbladet that the man's information was not consistent with other information regarding the incident.
“He gave us information about the incident, so he was not involved in it. He is charged with giving false information, but is not under any further suspicion,” Hekkelstrand told the newspaper.