Authorities suspect that an intense fire in a residential area of the northern city of Kemi on Sunday morning was started intentionally.
Lapland Police said on Sunday afternoon that they had taken one person into custody.
Fifteen people were evacuated as the fire destroyed a rowhouse on Purolankatu in the Marttala neighbourhood. The building included 12 apartments. The blaze started shortly before 6am.
Authorities issued a warning about heavy smoke spreading from the fire into the Purola and Karihaara residential areas. The alert was lifted around 10am.
According to police, all registered residents of the building had been contacted, and there were no reports of injuries.
Police were conducting an investigation at the scene, but did not announce any details on how or why the fire may have been started.
Law enforcement officials were carrying out technical investigations, as well as questioning residents, eyewitnesses and the suspect. Meanwhile firefighters were still monitoring the smouldering ruins in the afternoon.
Ten of those evacuated have been accommodated at a local hotel, as their homes were destroyed, according to the Oulu newspaper Kaleva.