The earthquake occurred at 02:57 GMT some 448 kilometers (278 miles) away from New Caledonia's capital Noumea. The epicenter of the earthquake was at a depth of 37.7 kilometers.
A Tsunami threat warning has been declared within 1,000 kilometers of the earthquake's epicenter, according to the US National Tsunami Warning Center.
"Tsunami waves reaching 1 to 3 meters above the tide level are possible along some coasts of Vanuatu ... Tsunami waves reaching 0.3 to 1 meters above the tide level are possible for some coasts of New Caledonia ... Fiji ... and New Zealand," the center said in a message.
Two aftershocks have been registered, both measuring in at magnitudes 5.9 and 5.4.
There have been no immediate reports of injuries.