An explosion shook the Swedish capital on Saturday, spreading fear among locals following another blast a little over a day earlier, local media reported.
The blast took place at an apartment building just past midnight in Stockholm, just a day after a major explosion that devastated another apartment building in Solna, north of the capital.
It is unclear if anyone died or was injured in the second explosion. There were reportedly no casualties from the first blast.
Police are trying to establish if there is a connection between the two explosions.
"It is far too early to say whether there is a connection. The work must be undertaken and the incidents are first investigated individually," Expressen quoted Towe Hagg, police spokesperson in the Stockholm region, as saying.
The National Bomb Squad is working at the scene, which has been cordoned off, and an ambulance could be seen at the site, the outlet reported.
About 20 people have been evacuated and around 70 windows were destroyed in the explosion, according to Expressen.
Monica Nielsen, a building resident, said, "I'm still in shock. I thought at first it was the war that had come, it was a huge explosion," local outlet SVT Nyheter reported.
Engineer Mikael Sundh, 40, was sitting at a computer next to a window when the explosion occurred.
"The entire window where I was sitting was smashed. There were blinds in the way, so maybe I got less (affected) than I would have otherwise," Expressen quoted him as saying.
Police are continuing to investigate who might be behind the explosion.
According to a police statement, at this stage no one has been arrested, but one person was questioned by the police.
Another two explosions happened this week at an apartment building in Astorp in Skane and later an apartment building in central Helsingborg.