The quake occurred at 10:55 pm and was located about 60 kilometers southeast of the town of Piteå in the Gulf of Bothnia. Many residents of the town and neighboring Luleå described feeling the quake.
Reports of the ground shaking have also come from as far as Böle, Älvsbyn, Boden and Nyborg in Norrbotten county.
After the earthquake, the area's emergency dispatcher center SOS Alarm was swamped with phone calls.
"This is an unusually large quake for Sweden. These kinds of quakes occur perhaps once every 10 years in Sweden," Uppsala University seismologist Reynir Bödvarsson says.
No damage or injuries were reported as of Sunday afternoon.