An earthquake measuring 5.9 on the Richter scale epicentred 24 kilometres southwest of Sofia was registered at 3 a.m.
No casualties have been reported, the Bulgarian News Agency, BTA, reported, quoting interior ministry data.
According to data of the Geophysical Institute with the Bulgarian Academy of Sciences, the earthquake was followed by more than 20 secondary tremors, two of which measuring over 4 on the Richter scale, BTA reported.
Emergency situation has been declared in the town of Pernik where damages to buildings have been reported. The wall of the nearby dam Studena is intact, an inspection by the Civil Defence found out.