"Based on the preliminary quake parameters, hazardous tsunami waves are possible for coasts located within 1,000km of the natural disaster epicenter", warned the Pacific Tsunami Warning Center (PTWC), saying waves could reach between one and three metres high.
New Zealand's Ministry of Civil Defence and Emergency Management, however, tweeted that there was no tsunami threat to the nation's coasts even though the tsunami alert issued for coasts within 1,000 km.
Those living on the west coast have been urged to remain vigilant.
The 10km deep undersea quake struck about 4am on Wednesday, 155km south-east of the Loyalty Islands off New Caledonia's east coast.
No damage has been reported in New Caledonia after a massive 7.5-magnitude quake struck southeast of the Loyalty Islands this evening.
A view of the bay of Noumea, the capital of New Caledonia, seen earlier this year.
Residents of New Caledonia received text messages directing them to go to refuges immediately.
No damage was immediately reported, according to Vincent Lepley, crisis coordinator for the Red Cross in New Caledonia.
The US Geological Survey (USGS) also recorded a series of aftershocks, two of them at 5.9 magnitude.
The Pacific Tsunami Warning Center confirmed tsunami waves had been observed following the quake.
Seismologists in Australia said they are monitoring the quake.
Nearly three hours after the quake, the Hawaii-based Pacific Tsunami Warning Center reported the threat stemming from the initial quake "has now passed".