Image: Risto Degerman / Yle

An earthquake measuring 3.5 on the Richter scale was reported just south of the western city of Oulu at about 12:30 am Friday, according to data from the US Geological Survey, which tracks earthquakes around the world.

The temblor's epicentre was recorded on the coastline of Liminganlahti Bay — about five kilometres east of the municipality of Lumijoki in Northern Ostrobothnia — at a depth of about 10 kilometres underground.

Rescue services and police received several calls about the night-time rumble, however no emergencies were reported and no units were sent out, according to local public safety officials.

Oulu's fire chief Marko Hottinen said he felt the ground tremble a couple of times within a few seconds. The rescue service department in downtown Oulu is located some 20 kilometres from the quake's epicentre.

Quake prompts tweets

Several local residents reacted to the bumps in the night on social media.

A Twitter user named Milka tweeted: "I thought I was going to have a heart attack when I heard what sounded like a snowplough going through the wall. The dog is still safely under the bed with toys."

Petteri Pyyni tweeted: "Yeah, that darn well was a real earthquake in Oulu an hour ago. As the whole apartment building was rocking, I thought the neighbour's bathtub had fallen downstairs."

Several earthquakes have shaken Finland in the past, according to the University of Helsinki's Department of Geosciences and Geography, but the temblor in Lumijoki was the country's most powerful quake since one that measured 3.0 in Kuusamo in the year 2000.

Not unique, but still rare

Kuusamo, which is about 200 kilometres northeast of Oulu, is another area in Finland known for seismic activity. The university's Institute of Seismology records between 15-30 earthquakes in Finland annually.

Seismologist Jari Kortström said that while Lumijoki's overnight earthquake was not unique it was still a rare occurrence.

The Bothnian Bay is a seismically active area but, according to Kortström, quakes usually take place under the sea or farther west in Sweden.

It is impossible to predict when or where an earthquake will take place, even through the examination of statistics, Kortström said.

But there are no catastrophic earthquakes expected in Finland in any case, he said.

"More powerful quakes are possible. An earthquake with a strength of 4.0 or more can cause structural damage to buildings," he said.