The quake prompted authorities in the French territory to order coastal evacuation after a tsunami warning was issued for nearby islands.
Several aftershocks have also rocked the region, which saw New Zealand also issue a tsunami warning.
There were no initial reports of immediate damage from the natural disaster.
A massive natural disaster has struck beneath the waters of the South Pacific, and dangerously powerful waves may soon follow.
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The Pacific Tsunami Warning Centre said there was no immediate risk of tsunami.
Judith Rostain, a freelance journalist based in New Caledonia's capital Noumea, said there was no damage to the city and that the threat of a tsunami appeared to have passed.
"Tsunami waves reaching 1 to 3 metres above the tide level are possible along some coasts of New Caledonia and Vanuatu", the PTWC said, warning of possible waves of up to one metre (three feet) for some parts of Fiji.
The epicenter of the quake was some 300 kilometers east of the capital of New Caledonia, Noumea, but such was the force of the shock that experts said small tsunami waves might be detectable as far away as Antarctica and Russian Federation.
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The epicentre of the quake was around 300 km (186.4 miles) east of the New Caledonia capital Noumea, but it was so strong that experts said small tsunami waves may be seen as far away as Antarctica and Russian Federation.
Mr Rene said so far there were no reports of a tsunami or damage in the Loyalty islands. "For now, nothing serious has happened".
A spokesman for the Vanuatu geohazards observatory said the sparsely populated island of Tanna was expected to be most affected but no evacuations had been ordered.
The PTWC warned: "A tsunami is a series of waves and the time between waves can be five minutes to one hour".
New Caledonia, a French overseas territory, has a population of about 259,000.
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