The United States Geological Survey downgraded the quake from an initial measurement of magnitude 8. It struck some 47km west of Arawa on the north coast of Bougainville Island at a depth of 154km, the USGS reported.
An initial tsunami alert for several Pacific islands was wound back to cover just PNG and the neighbouring Solomon Islands and the Pacific Tsunami Warning Center later said the tsunami threat had passed safely for those countries.
Quakes are common within the area which sits on the Pacific's "Ring of Fire", a hotspot for seismic activity due to friction between tectonic plates.
Loti Yates, the director of the Solomon Islands National Disaster Management Office, said people had been told to move to higher ground in Choiseul and Western Province.
Chris McKee, assistant director at PNG's Geophysical Observatory Office in Port Moresby, said there were no initial reports of damage or casualties from near the epicentre of the quake, which is sparsely populated.
The Joint Australian Tsunami Warning Centre earlier said there was no threat to Australia, and New Zealand confirmed there was no danger to its coastlines.