A 7.7-magnitude earthquake struck in the South Pacific on Wednesday, the US Geological Survey said, sparking a tsunami warning for New Zealand, Vanuatu, New Caledonia and other nations in the region.

The quake struck at just after midnight local time (1320 GMT Wednesday) about 415 kilometres (258 miles) east of Vao in New Caledonia at a depth of 10 kilometres, according to USGS.

"Hazardous tsunami waves from this earthquake are possible within the next three hours," the NWS Pacific Tsunami Warning Center said.

Waves reaching between 0.3 and one metre above the tide level are possible for some coasts of Fiji, New Zealand and Vanuatu, the centre said.

Smaller waves were forecast for other nations in the region including Australia, the Cook Islands and American Samoa.

There were no initial reports of casualties or damage from the quake, which was initially recorded by USGS at magnitude 7.5 before being revised to 7.7.

The Pacific "Ring of Fire", where tectonic plates collide, experiences frequent seismic and volcanic activity.