The USGS placed the epicenter of the quake near the city of Moca, in the northwestern end of the island.
Officer Guidiberto Torres Valle with the Moca Police Department said some parts of the city lost power, but service was quickly restored.
The Municipal Hospital in the city of Cayey treated a woman suffering from anxiety caused by the earthquake but no other injuries.
Araceli Vega, a nurse in the hospital, told CNN that she was treating a patient when she felt the building rattle, followed by a short moment of fear and confusion. Spanish Version of story
Additional Information Puerto Rico Trench.