The earthquake happened at 4:08 a.m. local time (0108 GMT) and was centered in the Golyaka district, the Turkish Disaster and Emergency Management Authority said, Xinhua reported.
The tremor was felt in Istanbul, Turkey's largest city, and other surrounding areas.
There has been a widespread panic in Golyaka, where the power has gone off, the NTV broadcaster reported.
Duzce province was hit by a massive magnitude-7.2 earthquake in 1999 that killed around 800 people.