A strong earthquake of 6.9 magnitude struck southeast of New Caledonia's Loyalty Islands on Monday, the United States Geological Service (USGS) reported.

The quake hit about 334 kilometres (208 miles) from Tadine in the Loyalty Islands and 455 kilometres from the New Caledonian capital of Noumea at 03:35 GMT, at a depth of 52 kilometres, the USGS said.

No immediate tsunami warning was issued.

Geoscience Australia said while the quake had a magnitude of 6.8 and a depth of 35 kilometres -- according to its own recordings -- it was so remote it was extremely unlikely to cause any damage.

"We don't have a threat (warning) from that," seismologist Clive Collins told AFP. "We don't consider it tsunamigenic... it's pretty much in the middle of nowhere."