A series of earthquakes have been registered in southwestern Bulgaria in the wee hours Saturday.

According to the Geophysics Institute at the Bulgarian Academy of Sciences, BAS, there have been 10 tremors, while the European Seismology Center has listed 13.

The first quake occurred at 1:24 am and the last – at 6:51 am at debts between 0.8 km to 4.9 km.

The strongest tremor has been registered at 3:21 am and had a magnitude of 3.9 points on the Richter scale.

There are no reports of casualties, damage, or panic. The shock was, however, felt by local residents with many spending the night outside.

The tremors were also felt in the town of Simitli and the nearby "Oranovo" coal mine, which collapsed on July 16.

Two miners died then and two others remain trapped inside with no hope to find them alive. Colleagues, looking for them, say they do not respond to their knocks on the mine's railroad tracks.

The rescue effort has been downgraded to search and is in its 12th day now. The teams have dug another 2 meters overnight from the 33-meter long detour gallery.

The earthquakes have not affected the works inside the mine where they were not felt as strongly as on the surface.

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