Three women were shot dead with a rifle in front of a restaurant in the small Finnish town of Imatra around midnight, police said on Sunday, Reuters reported.
A suspect, a 23-year-old local man, has been detained, the Southeastern Finland Police Department said in a statement.
The women were also local and the motive for the killings remains unclear, it said.
Police will hold a news conference at 12:00 GMT on Sunday, they said.