The European Earthquake Monitoring Centre recorded the quake's epicenter at a point 22 km (14 miles) northwest of the city. Its website quoted a witness as saying the quake was "strong but fortunately not very long."
Reuters correspondents saw people evacuating tall buildings in the sprawling city, and hundreds crammed into Athens's central Syntagma Square.
Two people were lightly injured by falling debris, health ministry officials said.
The Acropolis, a complex of ancient Greek buildings including the Parthenon located on a rocky hilltop overlooking the capital, was intact, according to the authorities.
Seismologist Manolis Skordilis told Greece's Star TV: "The earthquake was close to the surface, which is why it was felt so much."
A fire brigade official said there had been several calls asking for help in rescuing people trapped in elevators.
Around 40 minutes after the first felt tremor, residents felt another strong quake, which the EMC rated magnitude 4.4, with an epicenter in the same region at the foot of Mount Parnitha.In 1999, an earthquake of magnitude 5.9 in the same area killed 143 people.