The man has admitted to causing grievous bodily harm, reports NRK.
The 24-year-old has been charged with shooting for people at the Blå nightclub, the man's defence counsel Tore Even Gjendom told the broadcaster.
Two doormen, one bartender and a customer were injured in the incident. Two women are also believed to have suffered mild injuries as the result of ricochets.
The man, who is already known to police, has been charged with attempted murder, Oslo Police serious crime senior officer Grete Lien Metlid told NRK.
“It is a person we know well from before, a Norwegian man aged 24,” Metlid said.
Police arrested the man in possession of the weapon having already been alerted and on the way to the scene when the shooting too place.
“Police arrived promptly and did their jobs well. We have questioned a number of people and detained the man at the scene,” Metlid told NRK.
None of the victims are considered to be critically injured, according to the report.
“Four people have received wounds from shots. We cannot go into detail, but it is not critical or very serious for any of them, so things look good, relatively speaking,” Metlid said.
In an earlier press message, police wrote that the suspect was asked to leave the nightclub before he began shooting.
“We are working on the basis that there was an incident shortly before shooting, so will of course look into a possible connection,” Metlid said.
The officer added that the shooting was a “dramatic incident with many people present, so it is a serious case”.
Gjendom told NRK that it was too early to comment further.
Blå's manager Eyvind Brox called the shooting “incomprehensible and sad”.
“Nightlife should be safe for everyone,” Brox told NRK.