A 7.9 magnitude earthquake struck off Papua New Guinea (PNG) on Sunday, but there were no reports of casualties or damage after a potential tsunami did not occur. 

The United States Geological Survey (USGS) downgraded the quake from an initial measurement of magnitude 8. 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. 

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 in Papua New Guinea, 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. 

Australia and New Zealand both said they had assessed the threat and there was no danger to their coastlines. 

Bougainville Island is one of the islands that make up the Autonomous Region of Bougainville within Papua New Guinea (PNG) which is home to around 300,000 people. --- REUTERS