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

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 157 kilometres east of Rabaul.

The major tremor initially triggered a more widespread tsunami warning for the Pacific region, including Indonesia and the Solomon Islands, but that was pulled back after the US Geological Survey (USGS) downgraded the magnitude slightly from 8. It also revised the depth of the tremor to 103.2 kilometres from its original estimate of 73km.