People living along Papua New Guinea's coastline fled to higher ground after a magnitude-7.9 earthquake struck east of the Pacific nation, triggering a tsunami warning for parts of the archipelago.

Key points: A widespread tsunami warning was issued after the quake

A widespread tsunami warning was issued after the quake Warning was later cancelled after magnitude downgraded

Warning was later cancelled after magnitude downgraded There were no immediate reports of damage or casualties from quake

A couple of hours after the quake, the Pacific Tsunami Warning Centre (PTWC) said the threat had largely passed, although it said Government agencies should continue to monitor coastal tides.

"Based on all available data … the tsunami threat from this earthquake has now passed," the PTWC said in an updated and final alert after the quake, which struck 46 kilometres east of Taron.

The major tremor initially triggered a more widespread tsunami warning for the Pacific region, including New Zealand, Indonesia, Nauru and the Solomon Islands, but that was pulled back after the US Geological Survey (USGS) downgraded the magnitude slightly from 8.

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Australia's Bureau of Meteorology had said there was no threat to its coastlines.

Many residents in the northern parts of the autonomous region of Bougainville sought higher ground amid warnings that tsunami waves were possible.

"The town residents have vacated the whole place, those in the villages live higher up, so they're okay, it's just those near the coast," local resident Christabel Biasu said.

There were no immediate reports of damage or casualties from the quake, which the USGS initially measured at magnitude-8.0 and at a depth of about 100 kilometres.

A nurse at Buka General Hospital in Bougainville said the quake was so strong it felt like the building she was sleeping in would topple — she said patients were being moved a few kilometres to higher ground.

Residents in other parts of Papua New Guinea, including the capital of Port Moresby and Kavieng in the northern tip of New Ireland island, said they had not felt the quake, and no evacuation plans were in place.

However, senior seismologist Dan Jacksa said Papua New Guinea and neighbouring islands should prepare for aftershocks following the powerful quake.

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.

ABC/wires