The two blasts occurred just minutes apart and just a few hundred metres from each other in Husby, northwestern Stockholm, at around 2.30am.
One person was taken to hospital to be treated for minor injuries, and the buildings suffered considerable damage. Around 50 residents were evacuated while the buildings were assessed.
“My door just flew in by several metres. It was completely crushed,” a fourth floor resident told TT.
Police had on Tuesday morning cordoned off the surrounding area so technicians could work at the scene and investigate. They were also looking into whether there were cameras in the area, and speaking to witnesses.
“We don't yet know where the explosions happened, more than that it was close to or in the buildings,” said police press spokesperson Towe Hägg.
Police believe the two incidents were connected and have opened a preliminary investigation into so-called devastation endangering the public. “It was such a short interval between them, so we're investigating this as a single incident and we'll see if that changes during the investigation,” said Hägg.
Swedish newspaper Aftonbladet reports that the blast could be linked to an explosion in the upmarket Stockholm area Östermalm last week, but police could not confirm when approached by The Local.
“It's too early to say if we can connect it (with previous explosions), but we are of course trying to figure out if there are parallels with these different investigations that links them to the other detonations this past week,” police press spokesperson Ola Österling told The Local.
The incident is being treated as a so-called “special incident”, which can be launched to deal with a range of unexpected or sudden issues which the relevant police unit needs extra help and resources to deal with.
Additional reporting by Elias Liljeström for The Local.