Experts at the Bulgarian Academy of Sciences (BAS) have said that the discrepancies in the figures cited by different media outlets about the quake that jolted parts of the country early on Tuesday are normal.

According to reports of the US Geological Survey, an earthquake with a magnitude of 5.8 on the Richter scale shook Bulgaria's capital early on Tuesday.

The jolt struck at 3:00am local time, about 24km west of the city and at a depth of 9.2km.

The first quake was followed by a series of aftershocks, the strongest of which measured 4.2 - 4.3 on the Richter scale.

"You can trust whoever you like but, strictly speaking, the most reliable measuring of the size of the earthquake is carried out in the country where it struck," according to Nikolay Miloshev, head of BAS' Geophysical Institute.

The BAS' estimate of  Tuesday morning's earthquake is 5.8 on the Richter scale, the European Mediterranean Seismological Centre provides 5.6 on the same scale, the US Geological Survey cites 5.8 on the same scale and seismologists in Bulgaria's neighboring countries suggest a magnitude of 6.1 - 6.4.

Miloshev told journalists that it was impossible to provide more accurate figures by using one seismic station, as was the case in Greece.

He stressed that Bulgaria had seismic stations pointing in all four directions.

The expert defined the discrepancies in the figures as normal.

He reminded that in cases of strong jolts like the one that struck early on Tuesday, the quake was felt to be vertical near the epicenter and horizontal away from the epicenter.

Miloshev informed that the last strong earthquake in this region had occurred in 1965, measuring 4.5 on the Richter scale.

The expert suggested that a second strong jolt was not likely but added that "everything is possible since there can be no categorical forecast."

The researcher said that things appeared to be going back to normal.