The 7.4-magnitude quake struck about 130 kilometres (80 miles) south of the town of Kokopo in northeastern Papua New Guinea, at a depth of 63 kilometres (40 miles), the US Geological Survey reported, downgrading its original estimate that the quake was magnitude 7.5 and 10 kilometres (6 miles) deep.
The Pacific Tsunami Warning Center said hazardous tsunami waves were possible within 300 kilometres (186 miles) of the epicentre.
There were no immediate reports of waves being seen and no reports of damage, said Chris McKee, assistant director Geophysical Observatory in the capital, Port Moresby.
"The earthquake is offshore and the nearby land areas are fairly sparsely populated," McKee said.
The National Disaster Center also had not received any reports of damage, said acting director Martin Mose.
"We're just sending a message now to the area for villages along the coast to take extra precautions in case a tsunami is generated," he said.
Tuesday's quake was centred in the same area as two earthquakes that rocked Papua New Guinea last week. Neither of those quakes caused damage or generated a tsunami, but they were slightly lower in strength.
Papua New Guinea sits on the Ring of Fire, the arc of seismic faults around the Pacific Ocean where earthquakes are common.


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