Police in the western city of Kokkola have arrested a 21-year-old man on suspicion of deliberately starting a series of fires.
The first suspected act of arson was reported on Monday morning. Police said a wall adjacent to the main entrance of a Swedish-language youth club, Jungsborg, had been sprayed with a flammable liquid and ignited. There were people inside the building when it was set on fire, according to police.
On Tuesday, a paper recycling container was set alight at the Kattholmantie recycling depot and a little later, another container was ignited near a similar depot at a local Prisma shopping outlet.
Later on Tuesday afternoon, fire engulfed a deserted wooden house near the city's ice hall on Kaarlenkatu.
Police believe all of the fires were started intentionally, saying that eyewitness reports identified the same suspect in each incident.
A local man was taken into custody late on Tuesday evening and will be questioned on Wednesday.
The most serious charge relates to the fire at the Jungsborg youth centre, because the building was occupied at the time.