The quake struck some 168.2 km (104.5 mi) from the small town of Tadine of the Loyalty Islands, New Caledonia, United States Geological Survey (USGS) reported.
A major natural disaster Tuesday night struck the territory of New Caledonia, sparking tsunami alerts.
The warning identified vulnerable areas including Vanuatu's Anatom Island, Esperitu Santo; New Caledonia's Noumea and Fiji's Suva.
The undersea quake was only 10km deep, according to the Pacific Tsunami Warning Center (PTWC), and struck about 155km from the Loyalty Islands, off New Caledonia's east coast.
Authorities in the South Pacific territory urged people to move to locations more than 300 metres distant from the shore, and if possible, to sites higher than 12 metres above sea level.
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There were no immediate reports of damage from the quake.
Seismologists in Australia said they are monitoring the quake.
"Tsunami waves have been observed".
The New Zealand government's Ministry of Civil Defence and Emergency Management also said there is no tsunami risk to their country.
Meanwhile Australia's department of foreign affairs warned its citizens in New Caledonia to seek safety.
Both New Caledonia and Vanuatu sit on the Pacific "Ring of Fire", the arc of seismic faults around the Pacific Ocean where most of the world's earthquakes and volcanic activity occur.