Emergency services were called to a building in Skogås, Stockholm County at 21.30 on Sunday evening. Firefighters discovered heavy smoke on the fourth floor, but no fire.
Some time later the Swedish emergency services unit which deals with unknown chemical substances was called to the scene, as well as bomb technicians, tabloid Aftonbladet reported.
The incident, which was initially classed as public endangerment, led to parts of the local area being cordoned off. Sweden’s security police Säpo were even informed.
But after investigating throughout the night, technicians finally established that some form of narcotics manufacturing was behind the explosion.
“Some form of drug production has taken place in this apartment,” police spokesperson Lars Byström told news agency TT.
“We’ll see how we proceed with the matter now,” he added.
According to police, the smoke in the apartment was preceded by a bang, after which someone was seen running from the scene.
One witness told Aftonbladet that a burning pressure cooker was thrown from the building.
Between eight and ten people came into contact with the smoke caused by the explosion, with three sent to hospital. No arrests have so far been made.