The natural disaster struck roughly 167 kilometres deep, near Bougaineville Island - which is located in between Papua New Guinea and mainland Solomon Islands.
The Solomon Islands are regularly hit by earthquakes.
The USGS estimates that 72,000 people would have experienced severe shaking as a result of the quake.
There are no immediate reports of casualties or damage. It struck some 47 kms (29 miles) west of Arawa on the north coast of Bougainville Island at a depth of 154 km (96 miles), the USGS reported.
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Heavy damage to buildings and infrastructure is likely in an quake of that strength.
Earthquakes are common near Papua New Guinea, which lies on the 4,000-kilometre-long Pacific Australia plate.
Aloysius Laukai from Bougainville's New Dawn FM said the quake was strongly felt around the region, but there are no reports through yet of deaths, injury or major damage.
Papua New Guinea is located on the Pacific Ring of Fire, which is a zone of seismic activity and volcanoes around the edges of the Pacific Ocean.