A 5.7-magnitude earthquake jolted a large part of southern Greece on Friday but caused no major damage, according to preliminary data from the Athens Observatory.

The data revised an earlier estimate of a 5.8-magnitude quake by the EuroMediterranean Seismic Center (EMSC), while the US Geological Survey has put the magnitude at 5.6.

There have been no reports of casualties or damage caused by the temblor, which struck at around 6:45 a.m. local time (0345 GMT).

The epicenter was located about 150 km south of Athens in the sea off the Peloponnese peninsula at a depth of 80 km, according to the EMSC.

The earthquake was felt in Athens, Peloponnese and Aegean Sea islands.

The magnitude of the earthquake should not raise alarms, as the area is seismic prone and is known to give strong tremors in the seabed which do not cause major problems, said Professor Eythymios Lekkas at the Geodynamic Institute of the Athens Observatory.

Professor Gerasimos Papadopoulos, scientific director at the Geodynamic Institute, said the depth of the quake in the sea area indicated that aftershocks in the coming hours would be milder.

A 6.3-magnitude quake hit northern Aegean Sea in May, causing minor damage and slight injuries. The worst quake in recent years was reocreded in September 1999, when a 6.0-magnitude tremor hit Athens, killing about a hundred people.