The US Geological Survey says the quake today was on the island of New Britain in the Pacific.
The Pacific Tsunami Warning Center said the quake posed no tsunami threat. It also said the epicentre was 43 kilometres (27 miles) deep. Shallower quakes typically cause more damage.
The quake occurred about 130 kilometres from the city of Kokopo and 670 kilometres from Papua New Guinea's capital, Port Moresby.
Papua New Guinea sits on the Ring of Fire, the arc of seismic faults around the Pacific Ocean, and earthquakes are common.