Map of Bulgaria locating the epicentre of a magnitude 5.6 earthquake to hit the country.

A strong 5.8-magnitude quake that struck south-west of Bulgaria's capital Sofia shortly after 3.00am (00.00 GMT) on Tuesday made no casualties, Interior Minister Tsvetan Tsvetanov said.

“So far, there are no (known) casulties or injuries, which is good news,” Tsvetanov told Focus news agency.

“Let's hope it does not strike again. I know that people are in panic and this is only normal,” Prime Minister Boyko Borisov told Blitz news agency.

A crisis staff was formed in the town of Pernik, about 30 kilometres south-west of Sofia, where the epicentre of the shallow tremor was located, and police and firefighters were dispatched to the region, Tsvetanov told Focus press agency.

The Bulgarian Red Cross is also ready to step in where necessary, he said.

Pernik mayor Rositsa Yanakieva said there was no danger the big Studena 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 15 lighter aftershocks were registered after the first horizontal quake hit, which had a magnitude of 5.8 on the Richter scale, data by the Bulgarian Seizmological Institute showed.

The jolt was felt very strongly on the top floors of buildings in Sofia and panicked residents of Pernik kept calling the national radio stations and news agencies, which broadcast advice for people to stay outdoors.

Residents of tall apartment buildings in Sofia said objects crashed to the ground during the tremor which lasted several minutes.

“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.

People, who were still sitting outside in their pyjamas over an hour after the first jolt, said they felt new tremors around 4.30am (01.30 GMT) and 5.15am (0215 GMT).

The seismological institute measured them at 4.2 - 4.3 on the Richter scale, it said.

Civil defence chief Nikolay Nikolov said his service received many reports of toppled chimneys and cracked walls and even broken windows in the region of Pernik.

There were no reports of interruptions of electricity or communications.

The quake comes on the heels of Sunday's 6.0-magnitude earthquake around the northern Italian city of Ferrara that killed six people and reduced homes and historic buildings to rubble.

In August 2009, a 5.0 magnitude earthquake hit the Black Sea between Bulgaria and Romania to the southeast of the Kaliakra Cape, the Bulgarian seismological institute said at the time. No serious damage was reported. - AFP