The Pacific Tsunami Warning Centre issued a tsunami warning for coastlines within 300 kilometres of the epicentre, saying wave heights would vary depending on coastlines and that the initial wave may not be the largest.
It said small tsunamis had been detected and forecast waves up to one metre above the high tide level to hit parts of New Caledonia and smaller waves for Vanuatu.
"We are a little bit scared," said Wayan Rigault, communications manager at Hotel Nengone Village on the island of Mare, which is the closest landmass to the epicentre.
"We have had an earthquake last night and today it was quite a big one."
Mr Rigault said there was no immediate damage, but guests were on alert for a formal evacuation warning.
The quake — initially reported as magnitude-7.3 — was the second major tremor in the same area in less than 24 hours and the third in the past month.
Today's quake — the most powerful of the three — struck at 9:43am (AEDT) at a shallow depth of 10 kilometres, some 80 kilometres east of the Loyalty Islands, the United States Geological Survey (USGS) said.
Vanuatu's National Disaster Management Office advised people in southern provinces to evacuate coastal areas for higher ground.
New Caledonia's civil security agency said it was still compiling data, and was not planning to evacuate immediately.
Authorities in Australia and New Zealand said there were no tsunami threats to either of those countries.
Photo: United States Geological Survey/ RNZ. Caption: Quake off New Caledonia.