Residents in the area were warned to stay inside, but the object turned out to be a bag containing harmless objects, NTB reports.
“A security guard found a bag on Smalgangen [road, ed.] at around 10:30pm and called us. It was considered to be suspicious enough for us to close off the area,” operation leader Steinar Hausvik of Oslo police district told NTB at 11:20pm on Tuesday.
Police bomb experts were at the scene just before midnight and used two robots to open the bag.
Five hours after it was discovered, police were able confirm the object was not dangerous.
“There were a number of challenges getting to the bottom of it, but it turned out to be something completely harmless,” Hausvik said at 3:35 pm.
The bag contained tools, the police officer added.
Considerable resources were diverted to the situation in the early hours of Wednesday, with an X-ray machine also used by police to investigate the contents of the bag.
Newspaper Aftenposten reported a blinking red light had been seen on the black bag.
“Yes, there was a blinking light for which we do not yet have an explanation,” Hauvik said, adding that this was one of a number of factors related to police assessment of the object as potentially dangerous.
Pictures from the scene showed bomb disposal technicians in full kit with police guarding the area. Residents on the Smalgangen street were asked to remain indoors and the area around the location was closed off.
Last year, a home-made explosive device was discovered in the same part of the Norwegian capital when a 17-year-old boy, a Russian citizen, was found carrying the device. The 17-year-old was later sentenced to one year in prison. He has appealed the sentence.