The earthquake was centered in the town of Saruhanli, in Manisa province, at a depth of 9 kilometers (5.6 miles), the government-run Disaster and Emergency Management Presidency said.
HaberTurk news channel said it was felt in the neighboring provinces of Izmir, Aydin and Mugla.
Mayor Besim Dutlulu told HaberTurk that residents left their homes in panic but there were no reports of casualties.
The quake came a day after another temblor, measuring 5.4, shook the eastern province of Van, near the border with Iran, slightly injuring five people and damaging homes.
Turkey is crossed by two major fault lines and earthquakes are frequent. In 1999, a magnitude-7.4 quake killed more than 17,000 people in northwestern Turkey.