The quake hit some 77 kilometres north-northeast of Punta Cana, Dominican Republic, at a depth of about 68 kilometres, according to the US Geological Survey.
At least a dozen aftershocks have occurred since then, the agency said.
Puerto Rico and the Dominican Republic are located in a high seismic activity zone, given that the North American Plate and the northeast corner of the Caribbean plate meet in that area. (AP) GRS GRS