The alarm about the injured man, who is said to have been found outdoors at an address in the Grönaslätt area in Ronneby, was received by the police at half past three on Tuesday afternoon.
Police and ambulance services were sent to the scene and the man was taken to hospital.
Crime classification has not yet been set, but the police are investigating the incident as an attempted murder.
They are looking for a suspected crime scene and a stairwell in an apartment building is cordoned off.
The police currently have no information about the 20-year-old man's injury situation.
The text is updated.