© Volcano Discovery
The quake struck at just after midnight on Thursday local time (1320 GMT Wednesday) about 415 kilometres (258 miles) east of Vao in New Caledonia at a depth of 10 kilometres, according to the USGS.
"Hazardous tsunami waves from this earthquake are possible within the next three hours," the NWS Pacific Tsunami Warning Center said.
Waves reaching between 0.3 and one metre above the tide level are possible for some coasts of Fiji, New Zealand and Vanuatu, the centre said.
The New Zealand National Emergency Management Agency released a statement telling people in coastal areas to move away from waterfronts.
"We expect New Zealand coastal areas to experience strong and unusual currents and unpredictable surges at the shore following a magnitude 7.7 earthquake," the disaster agency said.
"People in or near the sea in the following areas should move out of the water, off beaches and shore areas and away from harbours, rivers and estuaries."
A map accompanying the statement indicated the affected areas included the far north of New Zealand's north island, the Great Barrier Island east of Auckland and a stretch of coast along the country's east.
The northern parts of New Zealand were the only areas in danger of any tsunami.
Agence France-Presse
Comment: Also of note the just before this major earthquake struck two magnititude 6 quakes hit the same area (both within an hour) according to the EarthTrack website. See here and here.
Two aftershocks of magnitude 6.1 have also been registered, see here and here.