A magnitude-7.9 earthquake has struck 46 kilometres east of Taron, Papua New Guinea, the US Geological Survey (USGS) reported, prompting a widespread warning about tsunami waves in the region.
"Tsunami waves have been observed," the Pacific Tsunami Warning Centre (PTWC) said, warning that waves reaching one to three metres above the tide level were possible along some of Papua New Guinea's coastlines.
It said any tsunami waves would hit within the next two hours.
The PTWC cancelled an earlier tsunami warning that encompassed Indonesia, the Solomon Islands, Pohnpei, Chuuk, Nauru, Kosrae and Vanuatu after the quake, which struck the New Ireland region of Papua New Guinea at a depth of 103.2 kilometres.
Any tsunami waves in countries other than Papua New Guinea were forecast to be less than 0.3 metres, the PTWC said.
New Zealand had earlier issued a tsunami warning, with New Zealanders advised to "stay off the beaches, stay out of the water, not go sightseeing and to listen to the radio and TV," a spokeswoman for the Ministry of Civil Defence and Emergency Management said.
However, New Zealand cancelled its warning after it was determined there was no threat to the country.
Australia's Bureau of Meteorology has said there is no threat to its coastlines.
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 73 kilometres.
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.