One quake, measuring 5.4 on the Richter scale, rattled the area south of the town of Agrinion, about 215 kilometers (134 miles) west-northwest of Athens, at about 6:17 a.m. (0317GMT).
Four hours earlier, at 2:27 a.m. (2327GMT), a quake of 4.7 magnitude hit the same region, with an epicenter 190 kilometers (118 miles) west-northwest of Athens.
No serious damage was immediately reported after either quake.
Greece lies in one of the world's most active earthquake zones. Last month the western island of Cephallonia was shaken by a moderately strong quake that caused landslides but no injuries.