The USGS said the tremor hit at a depth of five kilometres near the sparsely-populated East New Britain region, some 210 kilometres southeast of the town of Kokopo.
However, a tsunami warning was not issued by the Hawaii-based Pacific Tsunami Warning Center.
Papua New Guinea lies on the 4,000-kilometre-long Pacific Australia plate and earthquakes are common in the region.
It forms part of the “Ring of Fire”, a hotspot for seismic activity due to friction between tectonic plates.
(With PTI inputs)