A shallow 6.9-magnitude earthquake hit off the coast of the South Pacific island of Vanuatu late on Thursday, the US Geological Survey said, but there was no tsunami warning.

There were no immediate reports of casualties or damage.

The quake struck at a depth of 10 kilometres (six miles), around 122 kilometres west of the capital Port Vila.

It was followed less than an hour later by a 5.3 tremor at about the same depth.

Vanuatu lies on the so-called "Pacific Ring of Fire", a zone of frequent seismic activity caused by friction between shifting tectonic plates.

The Hawaii-based Pacific Tsunami Warning Center issued an information bulletin but no alert, saying "no destructive widespread tsunami threat exists based on historical earthquake and tsunami data".

The earthquake hit shortly after midnight (around 1300 GMT), USGS said.