The alarm about the detonation, which took place in Helsingborg, reached the police shortly after 00.30 night to Monday.
"Someone threw an object through a window that caused some kind of explosion," police say on their website.
The two people who were in the property should not have been physically injured. Both the police forensics and the National Bomb Guard have been called to the scene, which was blocked off.
The incident is being investigated as an attempt at murder, but further criminal charges can be added, police write.