Authorities said some empty houses, which had been abandoned by their inhabitants after suffering damage Wednesday, collapsed but no injuries were reported.
According to the Athens Geodynamic Institute, the aftershock struck as night fell Thursday outside the central town of Elasona, some 365 kilometers (225 miles) northwest of the Greek capital.
Local authorities advised people in the area to remain outdoors for a second night.
“We are advising people not to return to their homes in the area near the epicenter,” said Efthymios Lekkas, head of the state-run Earthquake Planning and Protection Organization.
“This latest event came from a section of the faultline that we had not considered to be active. It surprised us.”
The army set up tents in the area Wednesday after a 6.0-magnitude earthquake jolted the region and was felt as far as Montenegro, some 500 kilometers (310 miles) to the north.
It caused no serious injuries, but scores of homes were damaged in several villages near Elasona.