A 5.6-magnitude earthquake struck Bulgaria early on Tuesday near the capital Sofia, the U.S. Geological Survey (USGS) said, according to RIA Novosti.

The epicenter of the quake was registered at 03.33 a.m. local time (00:33 GMT), 23 kilometers (14 miles) west of Sofia at the depth of 9.1 km (5.7 miles).

According to Bulgarian officials cited by Reuters, the tremor shook apartment buildings in the capital and forced residents to flee their homes, but caused no damages or casualties.

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However, local media reported some structural damage, including collapsed building walls, in the western town of Pernik, which was the closest to the epicenter.

USGS also reported a 4.9-magnitude aftershock that occurred in the same location an hour-and-a-half after the initial tremor.

The recent quakes in Bulgaria and Italy indicate a sudden spike in seismic activity in Europe’s quake-prone Balkans region.

A 6.0-magnitude quake in northern Italy on Sunday killed seven people, injured over 50, and destroyed dozens of buildings.

Small aftershocks continued to shake the Emilia-Romagna region through Monday causing evacuation of at least 6,000 residents.