A 5.8-magnitude quake struck Bulgaria early on Tuesday, triggering panic among sleepy residents who ran into the streets in their pyjamas, and some minor damage, but no casualties were reported.
The quake jolted an area near Pernik, about 30 kilometres (20 miles) southwest of Sofia and was felt in the capital and other towns as well as in neighbouring Greece and Macedonia.
Residents of tall apartment buildings in Sofia said objects crashed to the ground during the tremor which lasted several minutes, and was followed by about 20 lighter aftershocks, according to local seismologists.
"Everything was shaking like crazy. I ran out shouting ... I won't go back home today," teenager Maria told AFP outside her apartment building in a western Sofia neighbourhood.
A state of emergency has been declared in the area around Pernik, a mining town of about 80,000 people, and police and firefighters were dispatched to the region to held distressed residents and check for damage.
School classes were cancelled on Tuesday and Wednesday.
"So far, there are no (known) casualties or injuries, which is good news," Interior Minister Tsvetan Tsvetanov told Focus press agency.
Civil defence chief Nikolay Nikolov said his service has received reports of toppled chimneys, falling masonry, cracked walls, broken windows and damaged cars in the Pernik region and Sofia.
However, there were no reports of any interruptions of electricity or communications and Sofia's airport was operating normally, as was Bulgaria's nuclear plant which lies about 200 kilometres north of the epicentre.
The quake comes on the heels of a 6.0-magnitude earthquake in northeastern Italy on Sunday that killed six people and reduced homes and historic buildings to rubble. National radio stations and news agencies broadcast advice for people to stay outdoors after being inundated with calls.
"Let's hope it does not strike again. I know that people are in panic and this is only normal," Bulgarian Prime Minister Boyko Borisov told Blitz news agency. Pernik mayor Rositsa Yanakieva sought to reassure residents that there was no danger that a major dam near the town could burst.
"The wall of the Studena dam is in good condition. It is being monitored constantly ... There are no reports of casualties or injuries in Pernik so far," Yanakieva said.
Over 20 lighter aftershocks were registered after the first quake hit, which had a magnitude of 5.8-5.9 on the Richter scale, according to the Bulgarian Seismological Institute.
Local people who were still sitting outside in their pyjamas over an hour after the first jolt said they felt new tremors before dawn which the seismological institute measured at 4.2 and 4.3.
Bulgaria's Seismological Institute chief Emil Botev said it was the strongest quake ever to hit the Pernik fault.
In August 2009, a 5.0-magnitude earthquake hit the Black Sea between Bulgaria and Romania but no serious damage was reported, while in 2004 a 5.5-quake hit downtown Sofia.
The deadliest was in 1904, when a 7.8 magnitude quake hit along the southwestern Struma river, killing over 200 people.