The blast happened at 1am at the street Gyllenstiernsgatan in the Östermalm area of the Swedish capital, but could be heard several kilometres away. It damaged the building and parked cars, with broken glass and other debris covering the area.
Erik Widstrand, head of the Stockholm City policing area, told a press conference at 1pm that the incident was being investigated as so-called “devastation endangering the public” but that no terrorism was suspected.
“It was one of the most powerful explosions we have had in this region,” he said.
The Local's reporter Tim Marringa was at the scene shortly before noon.
“The street is closed off with tape to keep curious local residents at a distance. The damage is clearly visible from behind the tape, and cars in front of the building were badly damaged,” he said.
“The police are keeping an eye on things while workers are replacing the broken windows.”
A police spokesperson told the TT news agency early on Monday that they believed “the explosion happened in or at the building, but exactly where is still unclear. There are damaged cars nearby, but the explosion probably didn't happen in them”.
TT photographer Anders Wiklund was at the scene on Monday morning and described the blast as “an extremely powerful explosion that was heard across all of Stockholm”.
The approximate location of the blast. Image: Google Maps
Ambulances and fire crews were at the scene, but there were no reports of injuries. Residents evacuated the building and were able to spend the night and get crisis support at a local school.
One resident told TT she was woken in the night by “an enormous blast” that shook her windows, and went to her balcony to see what had happened.
“There were fire engines already on the way, and then lots of police and ambulances came. We saw a large piece of metal, which may have been a door or part of a car, lying on the street. In the street lights, the broken glass was glittering and there was a lot of metal next to the cars, so we thought it must have been a car bomb that exploded,” she said.
She said that she was particularly concerned about the incident because of the school located in the same building, adding: “If it had happened a few hours later it could have been a total catastrophe.”
The school informed parents that it would be open as normal on Monday, but that the main entrance would be closed off due to police cordons.
The police bomb squad was set to examine the scene on Monday. Police opened an investigation into so-called 'devastation endangering the public', but at 7am it was still unclear what had caused the explosion.
Just two hours after the Östermalm blast, at around 3am, police were called to a loud explosion in the university town of Uppsala, about an hour north of Stockholm, damaging a building and vehicles parked nearby.
Police said they suspected “some kind of explosive charge had detonated” at Nedre slottsgatan in the town centre, but there were no reports of injuries.
There were no immediate indications that the two explosions were linked.