The youths arrested in the raids are suspected of being involved in illegal narcotics sales linked to organised crime in Oslo, reports NRK.
The arrests took place in the Follo region, which is part of the Akershus county to the south and east of the Norwegian capital.
Dealing and using drugs, extortion, violence, threatening behaviour and young women trading prostitution for drugs are among the activities connected to the arrests.
“Over time we have received a number of concerned reports from parents, schools and people who work with youths. This has led us to take action in this area,” chief inspector Lars Abelsen of the Øst police district told NRK.
Police have been monitoring groups in the area for up to two years in order to form an overview of their hierarchy before making arrests, according to the broadcaster's report.
The arrests were made during Tuesday and Wednesday with some 40 people from a police list of up to 50 names taken in for questioning.
The majority of the individuals are between 16 and 20 years old and from various social backgrounds.
Arrests were made at private homes and schools across Follo as well as in Oslo.
Abelsen told NRK that the raids were primarily concerned with dealing and using narcotics including cannabis, cocaine, ecstasy and MDMA, but that there was also an increasing trend for threats and violence in the monitored groups.
“It is often connected to someone that has sold drugs and owes money, and ends up with a debt to some of the heavier gangs. You are fined when you can't pay and it ends in a negative spiral. What we then see is that these gangs make threats and occasionally go through with their threats to show what they are capable of,” he said.
The police officer said that, on occasions, hardened criminals had knocked on the doors of family homes to make threats.
“We know that many of the people in these youth groups are scared of the criminal groups in Oslo,” he said.
Some of the arrested youths will be charged while others will be monitored by the Norwegian child protection service Barnevernet and other agencies, police told NRK. The raids are expected to continue for the next few days.